There should be a way to preserver your VIP days. Meaning you only one day if you log in.
Further Detail:
Let's say I buy like 600 days of VIP. Instead of it running for the next 600 days. It would only use 1 day everytime I log in. So I log in on jan 17 and I will use a VIP day for the next 24 hours. After those are up if I log in again it will use another. This way when people are on vacation or something they can keep those last few VIP days.