As a Naval Reservist let me give you some details.
Reservist at home get paid "drill pay" when they drill. A drill is a minimum of 4 continuous hours. Some groups meet one night a week for at least 4 hours. They are not allowed to exceed 8 hours. Some meet on weekends and get 2 drills in on each day. Drills are for training, either general or specific to their military specialty. Reservists are paid 1/30th of a month's pay per drill. They get zero allowances and duty pay unless their training involves something more dangerous like flight pay which is rare.
If you have to drive far enough to your drill site for a weekend of drill and you stay overnight (room and food at your expense unlike active duty) there are plenty of commanding officers that have no problem having you working that Saturday night
Much of the administrative matters take place on your own time. Lots of paperwork, preparing for training sessions, medical issues and of course keeping yourself in shape is on your time as well. One does enough Reserve activities in addition to the minimum 4 hour drill time to make it worth a day's pay. You don't know how bothersome those Reserve phone calls can be when you are at your regular job.
Think of it like NFL players getting paid for working on game day and not getting paid for the rest of the practices and meetings during the week. They are paid for the whole package of activities. I made more money when recalled to active duty in the middle east than I did in a 2 drill day as a reservist.