What type of starter are you planning to do? If you have a stirplate you can make one that is smaller and have it ready faster.
Mrmalty.com suggests 2.12L for a simple starter, 1.22L for intermittent shaking, and 1L with a stir plate.
If you use a stirplate you can go with 12-18 hrs (I go about 24) then chill for a day or so until the yeast drop out and compact on the bottom, then decant and warm the yeast up to pitch.
Both Wyeast smackpacks and White Labs vials DO NOT contain the optimum number of yeast cells to pitch in 5 gallons if the OG is over about 1.030.
It will ferment, you will get beer, but, it may not be as good as it could be.