Thursday is announced a day of mourning, for people killed on Monday, of course by Mousavi, and he has asked people to come out in number in black outfits. He could have done it for Wednesday. The pace of events is very fast, and he should do things and decide quickly! why Thursday? this gives the hardliners another day to think and organize, now it is a fight against the clock.
Friday will be a decisive day. Very good or very bad, this is my guts feeling. Khamanei the supreme leader will be holding the Friday prayer, he craves to announce a tough and brutal stance against the protesters, but before he could do that, militia or guards should resolve the issue of demonstrations on the street. That is why I think time is important, hopefully people can sustain the pressure peacefully till Friday and as somebody suggested even during and in the prayer sermon. That would restrict heavy handed reactions from Khamenei.
let's see