The thing this booking form reserves is a bay, for a length of time, and that is not how most garages here work.
Four bays: one and two on two post lifts, three on the four post lift, four flat with no lift for inspections and wheel work. When you book, one of them is held for the length of the job. The confirmation email says which.
The reason is the reason every garage customer already knows. A workshop that takes cars in the morning and works through them finishes some cars at nine and some at four, and nobody can be told which they are. A workshop that books bays can say the job is ninety minutes and mean it, because the ninety minutes has a room to happen in.
One exception, deliberately. Bay three is kept off the form until eleven every morning, for somebody who has broken down that morning. It sometimes sits empty. It is still right, because a garage with no give in the diary sends its own customers elsewhere on the day they most need it.