If Nirvana is unconditional then why is it not happening now?

The dependent origination are the cycle of happening/cessation conditions.

What is the dependent origination?

It is every true things, except nibbāna.

What is nibbāna?

It is the truth which is the opposite side of the dependent origination, the opposite side of the cycle of happening/cessation conditions. ์Nibbāna never has happening/cessation conditions. The conditions can know nibbāna, but they can't let nibbāna arise or vanish.

Why we can't see nibbāna by thinking like the noble ones can do?

Because we still having the wrong understood about the dependent origination, diṭṭhi-clinging, so we can't daily understand&discover&make cessation of the truth's root conditions, avijjā&taṇhā&all-unwholesome. Therefore we can't see nibbāna like the noble ones can do.

How to see nibbāna?

Observe sīla, meditate samādhi and vipassanā until enlightened.

The popular question about nibbāna already answered in Ekādasamo paricchedo Nibbānaniddeso of abhidhammāvatāra.

There also are many aspects of nibbāna in Abhi. Kathāvatthu as well.

The Dhamma is said to be timeless.

I think the Dhamma, specifically the first three noble truths, says that it's suffering (not nibbana) that's conditioned:

1. Truth of suffering
2. Truth of the cause/origin of suffering
3. Truth of the cessation of suffering

Nibbana is the cessation of suffering,

I suppose you could see the fourth truth (the noble eightfold path) as a cause of (or condition for) nibbana, but instead it's described as a path:

4. Truth of the path leading to the cessation of suffering

Is my wish or suitability a condition for it happen

The condition for (or path towards) the cessation of suffering is the abandoning of conditions which cause suffering; those conditions (according to the second noble truth), to be abandoned, are basically "craving" in various forms:

2. this is the dukkha·samudaya ariya·sacca: this taṇhā leading to rebirth, connected with desire and enjoyment, finding delight here or there, that is to say: kāma-taṇhā, bhava-taṇhā and vibhava-taṇhā

I think that, here (i.e. in SN 56.11) and elsewhere, it's taught that causes or origins of suffering include:

• Self-views, including identification with and attachment to the aggregates, even pride/conceit
• Sensual desires and attachment
• Aversion (maybe like 'desire' but the other side of the coin), also called "anger" or "hatred"
• Ignorance (as a result of which, wrong views and wrong attachments)
• Immorality
• Not just actual cravings, and attachments, but "tendencies" too

Conversely there are many factors which can help on the path.

• I'm not sure that merely "wishing" for something is sufficient to make it so -- e.g. SN 42.6:

  Very well, then, headman, I will question you on this matter. Answer as you see fit. What do you think: There is the case where a man is one who takes life, steals, indulges in illicit sex; is a liar, one who speaks divisive speech, harsh speech, & idle chatter; is greedy, bears thoughts of ill-will, & holds to wrong views. Then a great crowd of people, gathering & congregating, would pray, praise, & circumambulate with their hands palm-to-palm over the heart [saying,] 'May this man, at the break-up of the body, after death, reappear in a good destination, the heavenly world!' What do you think: would that man — because of the prayers, praise, & circumambulation of that great crowd of people — at the break-up of the body, after death, reappear in a good destination, the heavenly world?"

  "No, lord."

  "Suppose a man were to throw a large boulder into a deep lake of water, and a great crowd of people, gathering & congregating, would pray, praise, & circumambulate with their hands palm-to-palm over the heart [saying,] 'Rise up, O boulder! Come floating up, O boulder! Come float to the shore, O boulder!' What do you think: would that boulder — because of the prayers, praise, & circumambulation of that great crowd of people — rise up, come floating up, or come float to the shore?"

  "No, lord."

  See also How do you reach Nirvana when you are craving Nirvana? (for some analysis of wishing, of desire).

  But the second factor of the noble eightfold path is "right intention", "right resolve" ... a right or effective form (or result) of desire.

• It may begin with hearing the Dhamma, with taking refuge ... with morality (including e.g. generosity), with spiritual friendship

• See also e.g. the Wings to Awakening or Bodhipakkhiyādhammā

It's quite a lot of Dhamma and difficult to eradicate thoroughly ... so you might find it helpful to remember simplified versions like "suffering and cessation". Or just the first two noble truths: i.e. that "suffering is caused".

Let me answer with an analogy:

Suppose there is a small hill covering a much larger hill obscuring it from view. An energetic, skillful young woman climbs the hill (Stream Entry). She is happy about her achievement but suddenly realizes she has a lot more work left. She eventually climbs the larger hill and attains a magnificent view of the valley like never before. Her perspective of the surroundings has changed forever.

In this story, the larger hill was always there. But, she needed to create conditions to reach the summit.

Your question is like this sort of question, Think about a kid which is just started school, and he asks about this kind a questions from the his own class mates,

• What is Quantum Physics ?
• What is Universe ?
• What is General Relativity ?
• Can you explain wave function ?
• can you explain Schrodinger equation

i point out this questions cause even some collage students can not explain these for exact point, those who can will not explain it to those kids because there at another level far away from the kids. So for this example just think how can kid knows about all that things one may be willing to be lawyer, business men .etc and only one kid will be a scientist how will answer those questions soon he became one. Yet he also can not answer those questions, except he can say this book has this and that man said this, kind of answers.

so i'm telling here is if some one is on the path to achieve something extraordinary and noble,without going along that path see for our self is better, rather ask someone from same level,and it is useless. Because they maybe also on the path to achieve it, so their knowledge about it will also unclear not the exact.

Only possible explanation for Nirvana is we can not explain it. By following eight noble path anyone can see what exactly Nirvana is.

Hope you could understand.

Nirvana is suchness (tathata). This is why Buddha is called Tathagata. Suchness is when you don't crave for anything to be different than it is now. So, regardless of how your situation changes, you take it "as it is", at every moment in time. This is why Nirvana is called "unconditional", because it does not depend on the circumstances moment-by-moment.

But first you have to reach that state when you don't crave for anything to be different than it is. If you still have craving/aversion then Nirvana is not happening.

It's really simple.

@ Dheeraj Verma, you are continuously try to conceptualize the Nibbana. your inner mentality is keep you driving to fulfill your desire to feel,see or experience the Nibbana.Isn't it? I had this issue earlier. it's like blacksmith build his own cage more stronger and stronger and become prisoner in his own cage ignorantly. You build strong concepts,ideologies and conditions ultimately you will end up with depression and misery. this is not the path. I have faced this harsh reality and just cross the line. Just observe the nature and try to realize. Just carefully refer the life of Buddha how he observe the nature and then slowly and gently try to realize. Nirvana here and now. Metta!