It’s kind of hard to explain, but once you’ve already managed MeetMe and another booking apps, I guess if I give the north, you can try it out…
Well, the logic starts when I needed this
Why?
I dont have to check if a booking time is within, I have to check if the time I’m picking:
(Everything in my Booked table)
- Start picking time is on or before and is on or after Start time booked.
- Start picking time is on or before and is on or after End time booked.
- End picking time is on or before and is on or after Start time booked.
- End picking time is on or before and is on or after End time booked.
In my case I made a IF Then Else column to check both Start Times are available brings me the value 1, same to End Time.
A Math column to multiple both values, cuz if one isnt equals to 1, the multiplcation will be 0.
Finally, I create a Template to concatenate what you have more to check + If Then Else if it’s available (check the last column in the screenshot here down). Or in my case, brings me the value Space1 (we book coworker space in the app).
In the table where user is picking a time, we create a a Template column too, but with Space0, we have really to write “0”, cuz we wanna check only if a booking time it’s not available. And If Then Else column only to brings me those value only when start or end picking time is not empty.
So, a Relation tells me if this is available (empty) or is not (is not empty) 
@ThinhDinh as you also asked.