At the Poly last week it was 30 minutes before open. HS first bus was supposed to be at 9:30am. It ended up being there at 9:15am each of our two days. If we were at a busier resort I would have driven, but we never missed a bus.
Not sure where you’re staying but we’re at CBR and our buses have been awful. We haven’t been rushed for anything, but it’s been 30 min wait for internal buses, one bus an hour to get to Epcot/DHS when skyliner is down. AK and MK are more regular. The buses are supposed to start 30 min prior to park opening but from what I’ve seen, the buses are full and it’s been in consistent in another park bus following. If you want to be somewhere by a certain time, don’t rely on the busses right now.