Traditionally, couples left for their honeymoon immediately following the reception. Here's the good news: you can honeymoon whenever you want! Be it three days or one year later, when you choose to honeymoon with your better half is completely up to you.
You'll most likely be exhausted from your big day and may want to just veg out with your honey before jetting off to a well-deserved vacay- and that's okay. I always recommend couples take a day or two to relax and recuperate before leaving- it gives you time to pack, run last-minute errands and rest up for your big trip.
Do what works for you (and your sweetie),