[dsymonds]

Try having actual time ranges, not just slots, and you need to find, say, a 30m contiguous block of time.

[bobbles]

Also not on weekends, or outside hours during the week, also not at lunch time, though it may be 'free', also not 5PM, who's paying attention to a meeting then?

(just examples of what i might consider when setting up a meeting manually)

[karussell]

It is still just bitwise if you model the time slots e.g. like one bit stands for 5 or 1 minutes and then look for some contiguous 'free'-block in the result

[dsymonds]

Okay, how do you find a string of N 1's in a very long bit pattern? What's the space and time complexity of your solution? (hint: you can do a lot better)