Appointments in Clippie come in two shapes, and which one you get depends on how your groomer works.
You go to them: a time
If your groomer works from a studio or from home, you book a slot the same way you would anywhere else. Ten o'clock means ten o'clock — they are already where they need to be.
They come to you: a window
A mobile groomer is driving between dogs all day, and any single appointment can run long for reasons nobody could have predicted — a coat worse than described, traffic, a dog having a bad morning. A groomer who promises you two o'clock exactly is either going to be late or is padding the day so heavily that they can barely fit you in.
So instead you get a window — typically two hours — and it is not a hedge. It is calculated from the stops your groomer actually has that day and the driving between them.
You say when you are home first
When you book, you tell your groomer when you are actually available. The arrival window you get back always sits inside that. You are not being asked to keep a whole day free on the off-chance.
It gets tighter on the day
As the day takes shape, the window narrows, so you are not holding two hours open for something that is now clearly happening at half past ten.
If something changes
If your groomer's day slips enough to affect you, they will contact you themselves. Clippie does not send you an automated apology on their behalf — the person doing the work tells you what is happening.
Telling your groomer how matted your pet's coat is at booking is the single most useful thing you can do for the accuracy of your window: it changes how much time is set aside for you before anyone sets off.