As a night gamer, I don't believe this time constraint as 45 min. in a club. I think that there is no general timing in any kind of game. It can be 1 min. up to 45min. or more, it all depends to you and people you are interacting with. So for you, from my experience from night game I can tell you that u should find your time window. You will feel it when the time is good to take the number. It is like kissing. You feel the right moment and kiss the girl, there is no specific time. So it should be same as night in day game I think. When u feel that the interaction is ok than you can go for the number. Good luck.
NEVER GIVE UP, THIS IS YOUR LIFE->THIS IS YOUR GAME. ONE LIFE, LIVE IT.