How long do I need to keep my female cat crated post desexing?

The recommendation should come direct from your veterinarian actually but typically, it is recommended to keep a female cat crated in a small and quiet room for about 24-48 hours following the spaying operation. 

The idea is to keep the cat's activities limited for a few days to promote healing and to minimize the risk of complications. Although the duration for this will vary depending upon several factors including the cat's health and behaviour.

The environment should be comfortable and stress-free and that inside the crate or room there should soft bedding, access to water and the litter box and of course food. The litter box should be distanced from the food and water. The place should be quiet with limited interactions between the spayed female and other animals or children. She needs rest and quiet to recover. It's quite a big operation.

When the confinement period is over her activity levels can gradually be allowed to increase but once again it would be wise to seek your veterinarian's recommendations.

The general advice, on my research, is that vigorous activity and jumping et cetera should be limited including access to the outdoor environments until the incision has fully healed which should take around 10-14 days.

If you have any concerns about the recovery, you will no doubt contact your veterinarian for advice.