A tortoise can store sperm for years and only lay fertilised eggs if/when she feels the conditions are correct. This can cause additional problems when eggs are retained for too long and the eggs get over-calcified and become rough - making them far more likely to be retained to the point where they become stuck (known as dystocia or egg binding). If perfect laying conditions are provided, Mediterranean tortoises (the ones I have most experience with) will mate in the Spring and lay their eggs in early summer, so it can't be a long pregnancy - around 2 to 3 months on average. Incubation time varies from species to species. Why are you asking?