Do my minutes expire?

No. The minutes you buy do not expire.

You can use them today, in a month or next year, with whichever expert you prefer. You do not have to spend them within a window or buy again to keep them.

If you have gifted minutes and purchased minutes at the same time, the gifted ones are used first. That way the ones you paid for last longer.

The only way to lose your minutes is to delete your account, because that action erases your balance permanently.