The thing is, there are lots of unwritten rules about this:
Going to an Interview or board meeting - 15 minutes early
Catching a bus/train - 10 minutes early
Attending an organised class or activity group - 5 minutes early
Attending school or a work meeting, meeting up with a friend for a walk, joining an online video call - on time
Attending a kids party - on time or 5 minutes late
Attending any kind of function at a friend or family members' house - from a coffee to staying for a few days - 10 minutes late (no-one wants to be interrupted whilst they are doing a last minute wipe of the bathroom whilst brushing their hair).
For me, I tend to be on the on-time / late side.
Given the above, you should also prepare yourself with the requisite refreshments, indoor/outdoor clothing and activities to pass the time and and where needed if indeed you find yourself to be early.