“The second one, but make it 7:30”

Changing the time should preserve the rest of the booking.

Conceptual physical control panel: a rotary selector labelled SELECT chooses among three positions. A separate lime confirmation button labelled CONFIRM is beneath a closed transparent safety cover. Choosing and committing are separate actions.

A person asks an assistant to find a restaurant for two at 7. They look at the options and say: “The second one, but make it 7:30.”

It sounds like a small change. But now the assistant has to keep the restaurant and party size, change the time and check availability again. The booking shown for confirmation needs to say 7:30.

If that time isn't available, we need to come back with the remaining options. Booking at 7 anyway would ignore the request. Asking the person to start again would lose everything they already told us.

This is where I find it useful to work through the actual conversation. “Book a restaurant” looks simple on a feature list. The person changes one detail halfway through, and suddenly we have to decide what stays, what changes and what needs checking again.