An FBI Agent and a bank robber are trapped in a building that will explode in 120 minutes and both of them will have to work together.

I like the idea. Could be interesting to watch. Not too sure about the title though. The characters, or at least one of them, need to have their goal stated in the logline. Also, who is trying to stop them? Who is the antagonist? Who set the explosives? If it was the robber, he should be able to disarm them easily enough. It can't be to break into the vault (if the building is a bank) because then he can't be a good bankrobber if he uses so much explosives that he will blow up the entire building, including himself, and not have a way to disarm it without the help of an FBI agent I assume is there to catch him. ... And speaking of witch, what building is it? Is it a bank? Is it FBI headquarters? Somewhere else?

How about:

A zealous FBI Agent is forced to work together with the elusive bank robber he's spent his career trying to catch, in order to escape the bank they've become trapped in, with a bomb set to explode in two hours, by an escaped terrorist that the Agent sent to gitmo.

I don't know if that is your story. But at least you can work with that and make it fit what you had in mind.