According to Protestant belief, when did Jesus present His blood into the Holy of Holies as required by Law?

Wouldn’t this have been necessary for man. Jesus was not just man but God. The veil tearing in two shows me that this was not something Jesus needed to physically do within the temple as his own blood was spilled for our sins, the location of the blood doesn’t seem relevant since he is literally part of the Holy Trinity. He is literally the Holy of Holies

Entering the Holy of Holies in the Old Testament occurred once per year on the day of atonement. See also Lev 16:29-34.

Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation unto you; and ye shall afflict your souls, and offer an offering made by fire unto the LORD. Lev 23:27

That would be the general pattern of the reality in Christ Jesus. I say "general" because while the Old required annual sacrifices, Christ did this once for all time never to be repeated. He does not suffer often.

For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself. Heb 9:26

But when did entering the heavenly Holy of Holies take place? Was it during His time in the tomb, ascension 40 days later, or some 6 months later at Atonement day or centuries later? Or does the bible tell us?

Recall the event between Mary Magdalene and Christ in the garden after He rose out from the dead.

Jesus saith unto her, Touch me not; for I am not yet ascended to my Father: but go to my brethren, and say unto them, I ascend unto my Father, and your Father; and to my God, and your God. John 20:17

Touch me not because He had yet to ascend to His Father. This is an oblique reference to the High Priest at Atonement.

And there shall be no man in the tabernacle of the congregation when he [Levitical High Priest] goeth in to make an atonement in the holy place, until he come out, and have made an atonement for himself, and for his household, and for all the congregation of Israel. Lev 16:17

In other words, Mary should not have been present, let alone touching Him. However, once He completed atonement, it was perfectly fine to touch.

Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side: and be not faithless, but believing. John 20:27

There is one other piece, the requirement that the one making a Testament must die before it is in effect.

For where a testament is, there must also of necessity be the death of the testator. Heb 9:16

Christ made the Testament at the Last Supper and death. And then resurrected for our life.

So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation. Heb 9:28

So, to answer the OP from this Protestant point of view, when did Christ enter the heavenly Holy of Holies?

Within minutes of His resurrection, He ascended into the heavenly Holy of Holies.

TO ADD: Christ is explicit about the timing of ascending to God in John 20:17. He tells Mary, I ascend.

Jesus saith unto her, Touch me not; for I am not yet ascended to my Father: but go to my brethren, and say unto them, I ascend unto my Father, and your Father; and to my God, and your God.

"Ascend" is in the present tense. She leaves, He ascends.

Yes, that same day He also descends back to earth.

Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace be unto you. John 20:19

Later the same day, He shows them His wounds to prove Himself who He is.

At no point did Jesus Christ present his own blood in the most holy part of the earthly temple in Jerusalem. The book of Hebrews shows him ascending in glory to the Father in heaven, and there presenting his blood. The whole of chapter 9 goes into this. The first 7 verses speak of earthly animal sacrifices, with the High Priest entering but once a year into the Most Holy, with a bowl containing blood, which he offered for his own sins, and those of the Israelites. Now comes the link to Jesus Christ:

"The Holy Ghost thus signifying that the way into the holiest of all was not yet made manifest, while as the first tabernacle was yet standing: which was a figure for the time then present, ...until the time of reformation. But Christ being come an high priest of good things to come, by a greater and more perfect tabernacle, not made with hands, that is to say, not of this building; neither by the blood of goats and calves, but by his own blood he entered in once into the holy place, having obtained eternal redemption." Hebrews 9:8-12 A.V.

There is no mention of a bowl (or scarlet wool or hyssop) when the risen Christ offered his blood in the throne-room of heaven. The reason why not is contained in the following verses:

"It was therefore necessary that the patterns of things in the heavens should be purified by these [sprinkled blood of animals] but the heavenly things themselves with better sacrifices than these. For Christ is not entered into the holy places made with hands, which are the figures of the true; but into heaven itself, now to appear in the presence of God for us." (Ibid, vss. 23-24) [Square brackets and bold italics mine.]

Christ did not enter into the Most Holy part of the temple in Jerusalem at any time during his earthly life, or after his death. As for, "as required by Law" (in the question) that Law only pertained to the earthly things prior to the once-for-all-time perfect sacrifice of Christ. At the point of his death on the cross, the immensely thick, woven tapestry in the temple on earth was supernaturally rent asunder, from top to bottom, signifying the spiritual way now being opened into the very presence of God - Christ being the one to first enter in to the heavenly reality.

Bear in mind what happened to the Law at the point of Christ nailed to the cross:

"Blotting out the handwriting of ordinances that was against us, which was contrary to us, and took it out of the way, nailing it to the cross." Colossians 2:14 A.V. [Bold mine]

This means that the requirements on earth for temple sacrifices had permanently ended, for God's people. Therefore, the risen Christ could go to heaven to present the value of his shed blood. We are told a few verses further on (in Col. 3:1) that Christ was sitting on the right hand of God. So, the answer to the question is that at some point after Christ died on earth, he ascended to stand before God, presented the blood of the new covenant, then sat down at God's right hand. That can be narrowed down to Jesus telling Mary on the morning of his resurrection not to cling on to him, for he had not yet ascended to the Father (John 20:17). Some Protestants may have pinned it down to a more exact time, but it is the fact that it happened, unseen by us, in heaven, that should be all of our consideration and joy.

My reading of the chapter in Hebrews is that his version of "entering the Holy Place" was entering the presence of God. "For Christ has entered not into a sanctuary made with hands, a copy of the true one, but into heaven itself, now to appear in the presence of God on our behalf" (v24, RSV) He gained access to this real sanctuary by his own blood (v12), whereas the ordinary priest can enter only the "copy" sanctuary, the physical sanctuary, "with blood not his own" (v25).

If we are obliged to define a timing for these events, we might identify the moment of "entering the sanctuary" with the Ascension, when he reaches the presence of his Father in a more direct sense. In which case, that would also be the moment when he "presented the blood".

Though it might be better to regard it as a timeless event, associated with the fact of Crucifixion-and-Resurrection.

I don't think this is a peculiarly Protestant interpretation. Just a scriptural one.