"Always" is an impossible answer, "sometimes" is too vague. I wish there was a "most of the time" option.
When I say I'll pray, I try to do it immediately, before it can slip my mind, and when it is needed most. If I wait, the situation might be already resolved and my prayers would be too late.
I have a friend who says that retroactive prayer (prayer after the situation is resolved) works. He once wrote a letter to his sister asking her to pray about a delayed flight, knowing that she won't get the letter for days after the flight took off, but said that since God is not limited by time, He could answer her prayer retroactively and make the flight on time!
Cool idea, but how do the rest of you feel about the idea?