Depends on the product. However, general guide lines are at 2 weeks, 5 weeks, 8 weeks and 12 weeks.
Oh Oh! Caution! You should NOT worm them! A vet should! When you worm an animal it is best left to a vet simply because worming medicines are toxic poisons which cause the worm(s) to die thus making all pets sick for a day or so! You CAN inadvertently kill your pet! So beware! Products purchased over the counter can kill or make your pet sick, and not kill the parasite! So please use caution! Also, worms can quickly kill any kitten or pup or baby creature much more quickly than it would any adult species.
My kitten is 3 months what do I need to do?