A named hour, booked while the evening is still going
A named hour is a booking for a stated time later in the evening rather than the next available one, so she sets out to reach you at the minute you chose.
There are two ways to write a booking. The first asks for the next available hour, and the arrival window of forty to sixty minutes runs from confirmation. The second names a time: ninety minutes at 23:30, say, written at a quarter past nine. She then sets out to meet that hour rather than the moment the booking was agreed.
Why it suits a long evening
A named hour moves the whole exchange to a calmer moment. It can be arranged at the start of dinner, in the interval of a show or before the first round, while you still have both hands free and a charged phone. Any deposit is settled then too. After that, the phone can go into a pocket for the rest of the evening, and there is no need to watch the clock at the table.
How far ahead
As far as you like. A named hour booked the same day is an ordinary booking. One booked more than twenty-four hours ahead carries a deposit of half the fee, as does a first booking with the house, whatever the gap.
Choosing the hour
Choose it for the slow version of your evening, not the quick one. If you think dinner will end at half past ten, name the hour on the assumption that it ends at a quarter to eleven. Moving a booking earlier is easy to ask for; moving it later works while she has not yet set out, and costs nothing when she can keep the new time.