Just rooted around the FAQs and came up with some answers for you. Every member starts out with 7 days vacation. You get 2 more days every month up to a maximum of 30 days for standard members. Gold gets up to 60 days and diamond/platinum get up to 90 days. The other vacation difference between standard and premium is standard have to manually go on vacation, but for premium members it kicks in automatically if you're in danger of losing a correspondence game on time.
All 3 levels are considered premium, but there are differences between each level. Amazing what you can find with a few mouseclicks, eh?
Hey, does anyone know if premium members get handed more vacation time than members who are playing for free? Now another question, my friend who is going to join chess. com wants to know that in order to be a premium member, do you have to be a gold member or at least a platinum member. Thanks.