Yep, Heavy has it correct.
You can wait 2-3 days, but still come off ass needy because when you're in that moment you can still project that vibe.
When I number close a girl, I ALWAYS TEXT IMMEDIATELY. Because then she will save my number in her phone, and will remember who I am.
If you wait long, her mood will change and it will be different from her mood during the interaction.
So when I'm running day game, I'll say something like "Lets go out sometime." And she'll be like "yeah for sure." Then I whip out your phone and tell them to put their number in. I'll talk for a few more secs, hug + kiss on cheek for goodbye. Then IMMEDIATELY send "It was nice meeting ya cutie - Name"
When I'm out at night... shit goes haywire. I'll usually get like 5+ numbers that night, however I won't text immediately. I'll wait until I'm free or when the club closes and I'll send a MASS TEXT. "Hey it was nice meeting ya cutie. Get home safe. -Name"
They'll do three things, "Thanks! Nice meeting ya too

." or "What are you up to?" or not reply at all.
The first one you can game later, the second one you can fuck that same night, and the third one you can game later.