The published start time is for the closed event practice. For season races, you can only join the server for closed practice if you have signed up and have a confirmed place on the grid.
Some people will have been able to practice at other times during the week and may not join until qualifying. Some may have life commitments that mean they are joining just before the race start.
Just stick around – you may be alone if you join at the start of closed practice, but you likely won’t be by the time the race starts! Remember too that if everyone who wants to race joins and leaves because they think it’s quiet, the grid WILL be quiet!