Queens don’t ovulate until they have been stimulated by the first mating. It is important to know this mating date in order to calculate the first possible due date of your kittens.
A queen's gestation period is generally 65 days long, but it varies with breeds and individuals. A couple of days before giving birth my queens are usually a little clingy and restless, so I make sure the birthing box is already in place and available to them. I also have my birthing kit, extra towels etc. and some food and drink nearby. Don’t forget to have food and drink available for yourself too.