First of all, for your spouse to be able to pick up the car, the reservation should be made in the name of your spouse, and you should be added as an authorized driver. Your spouse won't be able to pick up the rental if it's booked in only your name.
If the first condition is met; for rentals that were paid for ahead of time, the car will be held for up to an hour during business hours after the scheduled pickup time. It may be honored at any time during the rental period that was bought, though. Do not forget that the type of vehicle might not be guaranteed after the 60-minute grace period.
For reservations where you can pay later, the car will also be held for up to an hour during business hours after the scheduled pickup time. If you are past this window and haven't told Sixt about the delay, there's a chance that you might not get a car.
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