On our trips, we usually do VB as a morning or two (for a week long trip). The crowds there are far better if you get there when they open. Easier for us because we always stay at Cabana Bay which has its own entrance to VB..
I'd say start day 2 at VB when they open and maybe leave around lunch time. Or, if you are loving it there, stay and have lunch and enjoy it longer. Either way, you can spend your afternoon/evening hours back at one of the other parks.