Availability Calendar for small web application

Existing web application with [login to view URL] calendar needs enhancement so user clicks a date on calendar, then a dropdown displays with list of available times between open/close business hours and subtracting any events in calendar already. SPECS - Configurable business hours (Open/Close) using [login to view URL] - Configurable appointment length, default 1 hour using [login to view URL] *** Changes to business hours / appointment length will only impact future events. No logic is needed to change existing events *** When a User clicks a date in the calendar, a dropdown will be shown below the calendar with available time slots. Timeslots will be every hourly time (using appointment length value) that does not conflict with existing events in the calendar. EXAMPLE 1 - User chooses Friday, Sept 2, 2016 - Existing Events (9am - 10am, 1pm-3pm) - Business Hours for Friday 8am - 5pm - Appointment Length = 2 Dropdown would show following values: * 10AM - 12PM * 3PM - 5PM EXAMPLE 2 - User chooses Saturday, Sept 2, 2016 - Existing Events (9am - 10am, 11am12pm) - Business Hours for Friday 8am - 4pm - Appointment Length = 1 Dropdown would show following values: * 8AM - 9AM * 12PM - 1PM * 1PM - 2PM * 2PM - 3PM