Premium membership doesn't increase your vacation time, just the maximum amount you can accumulate.
There is some information in the pop-up tool-tip on the membership page that mentions premium members get more vacation days but I don't think that is the case anymore; especially since it isn't touted as a member benefit anywhere I have been able to find outside of the tool-tip. The only thing mentioned in the FAQ is the cap, 7 days initial vacation, and 2 days a month accrual (one on the 1st and one on the 15th).
I recently got a diamond package and i expected my 2 days 13 hours vacation time to go back to 90 days. I had this high hope because i would be out of town without any internet for a week and i could save my 3 day games as well. But the case is that my vacation time still remains at 2 days 13 hours. Why is that? is there any way to immediately "boost up" vacation time?