Business contacts: how long to wait before the follow-up?

Kind of a strange question, but this stuff isn't exactly second nature to me.

So:

You meet someone at an event (their event). You offer them your (photographic) services. They say, "Great. Call me."

Taking into consideration that this person probably talks to literally hundreds of other people a day, how much time should you wait (or not wait) to make that follow-up call?

I've heard everywhere from "no later than 48 hours, because the emotional connection that was forged upon their initial meeting with you will dissipate rapidly as the days pass " to "one week, to communicate that you've got a lot more going on besides them." Where do you think the truth lies? What do you feel are the thresholds for "too soon" and "too late?"

Yes, there is a specific reason I'm asking. Any thoughts appreciated!

I usually try to find out when the best time to call/email them is. If I don't get that information I usually call sometime later the next day or the day after. That way they (hopefully) still remember talking to me about photography.

Usually I see "Great. Call me." as a possible no thanks.
But more of a maybe than "I'll call you" when they never do.
It's a lukewarm contact, that you need to get to a hot lead by calling them !

"one week, to communicate that you've got a lot more going on besides them."
That seems to me like a good way to lose business.

My work is more a writer than a straight photographer, although I do both, but I always follow up the next business day, and then if don't reach him/her leave a call-back. One week later, if no return call, then I call again. After that, I'm done ...