Premium candy packs are the membership packs, you will have to login every day for the duration of the pack to receive the reward. This means that if you fail to login during the time period, that that day’s “offer” or “value” of candy is lost. During the premium candy activation period, you can only purchase the same candy packs to “extend” the premium packs.
However, the VIP exp is given immediately for the full amount of candy packs. This means that if you really want a VIP level perks, getting 1~2 packs of 30 day premium pack can bump you quite a bit with the least amount of investment.