There are two rules you must follow in this.

Rule 1: The industry standard minimum waiting period is 2 days. For example if you get a number on a Friday, the soonest you can call is the following Sunday.

Rule 2: Initiating the making of plans for dates 1 through 3 with a new girl expires at 5:00 pm on the Wednesday before a weekend. Anything after that is technically a booty call.

Based on these rules, the sweet spot is Tuesday evening or Wednesday before 5:00 pm.