I say half hour incase time over runs, I’ve had this happen before so let’s say 30 mins turns to 40 or 45 then that’s how punters can be left hanging outside.
Over runs are different to SPs having a gap between punters [its punters wanting to extend most times]
Thats like a garage doing car servicing instead of allowing say 10-15 mins between motors to provide some flexibility instead downing tools to take this up to 30, 40 or 45 mins as you reference
Its not gonna happen
If you are left hanging outside its your own fault, for not walking
It happens more when you have booked shorter sessions especially 15 mins
Some SPs have form for this & reporting is often provided on here
The approach to be taken differs depending on whether you wanna revisit said SP
If you dont then no response is ideal radio silence as they'll waste time trying to figure out if you are coming or not, like they've wasted yours
If you do & you've got plans B C etc concentrate on these
& a polite text [sorry i had to go ... blah blah] can yield some upside as i've found when the session is re-arranged, even tho it is annoying at the time
