How do the slots get calculated?

My cargo company is based in Dubai (Meigs) and I wanted to switch out aircraft on a route. I cleared the schedule of aircraft A and went to put aircraft B on that route but it was showing 100% for those time slots. When I clear a schedule shouldn’t those slots be added back into the pool? I have several other aircraft I was thinking of swapping out and now I’m worried I’d lose those slots.

I guess you where unlucky. In the time you needed to swap A/C someone else probably took your slot.

That’s impossible. It was probably under 20 seconds.

Is it the same aircraft type at the same time? The safest way would be to add the flight without deleting the old one. You can do this with the existing flight number function on the schedule screen.