You accrue a certain percentage of the hours you work. It will never expire. There is a cap on how many hours you can accrue, but it is a rather large number. If you ever get close to the cap, you can use the hours for mental health days and get paid for them.

no

It all rolls over but only 80 hours are kept as protected sick time and the rest are extended sick time. I honestly don’t know the difference.

sick time will roll over but vacation time does not rollover, if you don’t use it by the new year it will be paid out