Adding New Time slots to Time slots table

I am working on party booking system where user can schedule his party by entering time slot. if user enters time slot which is between the existing time slot then that should not be added. For Example:we have 10:00 Am to 12:00 PM a booking and if new user need to book a party then the time slot table should not accept time between 10:00 am to 12:00 PM and it also should not accept 9:30 am to 11:00 am and also should not accept 10:00 am to 12:30 Pm and also 10:00 am to 11:00 am