Create variety of time slots

Newbie here! I'm creating time slots for a booking app which will all vary in length (15 mins / 45 mins / 60 mins). I have set it up as 15 min slots throughout the day, so depending on the type of booking a customer selects will determine the length of the slot needed.  I need to somehow add these 15 min slots together to create 45 min slots (the times also need to be directly after one another, 9am, 9:15am, 9:30am otherwise it needs to skip that time slot and leave it as a 15 min slot).  It's quite complex and has a lot of business rules that need to be included. This is how I am currently creating my 15 min slots. Any help is much appreciated :)   
1 answers

Make an Appointment entity. An Appointment can be associated with 1 up to max 4 (up following) Timeslots (based on your 60 minutes description in OP. I think you should give your Timeslots an autonumber attribute. Thay way you can easily retrieve the necessary Timeslots from database with a ‘Retrieve from database’, with custom Limit/Offset in combination with sorting on the Autonumber.