score:4
I don't have any references for this (most rainfall charts don't go down to the hour of the day...), but yes, based on living in Singapore for years, there is a general pattern to rainfall in that area of the world. It goes like this:
So the TL;DR would be that if you're going to hitchhike in the rainy season, it would behoove you to get on the road as early as possible and try to finish up before the afternoon. Which is actually good advice when hitchhiking anywhere, lots of long rides in the morning and it gives you some buffer until darkness closes in.
Now obviously this is only a rough pattern, and particularly in the rainy season, it's fairly common to have spells of several days when it rains pretty much non-stop. But if it's sunny when you wake up, hit the road and make the most of it.