On our first Magic Kingdom day (Monday), the first bus picked us up at 7:45. Every family got on. We arrived just as temp checks were opening, so we were in the first of the crowd heading to Mine Train. We maybe waited 3-5 minutes for it (walking the whole time). On our second Magic Kingdom day (Friday) the bus didn't come until 7:53 and there were two scooters that needed to load. By the time the driver loaded both of those and filled the bus, there was quite a crowd. Not everyone got on, but another bus was pulling in behind. Not sure if everyone got on that one or not. By the time we got to Magic Kingdom everyone was in, and the line was already pretty established at Mine Train.