Phlebotomy, seen 40 mins after appt. slot.

Summary: Phlebotomy, seen 40 mins after appt. slot.

My daughter booked in an appointment with phlebotomy at Prince Street clinic in Waterloo at 8.30.
She booked the appointment then so she could be on time for work at 9am (works from home).
The clinic didn't open their doors until 8:35 then my daughter was seen by the phlebotomist at 9:10 and this was only after I spoke to the receptionist on how long it was taking, and apparently "the screen is not yellow " was the reason for the delay.
My daughter is now very late for work and will be reprimanded for this.
Whilst I understand that delays can happen, what is the point of having time slots allocated when they are not adhered to.