Find if a contractor is free in a give time slot. Contractor will add / remove a time slot in which they are busy during the day.
For example.
Contractor adds these time slots as busy - 10:35pm to 11:40pm, 10:00am to 12:15pm, 12:30pm to 1pm (unordered)
isContractorAvailable(10:00am, 11:00am) -> false
isContractorAvailable(9:00am, 10:00am) -> true

Note - all the time slots will always be within one day (00:00 to 23:59)