Do not stick to time slots even when you are sitting there on time and waiting for your selected technician to finish their current job.
On several occasions one particular staff member whose name I can’t recall has intentionally put a walk-in customer ahead of me whilst I have a booking, stating that they have somewhere to be, Not considering that I have booked a specific time slot and also have somewhere to be. If you mention this she will try to justify her actions in front of the whole shop