My father went thru the same thing when he had his garage built back in 1988.
The basic garage was finished, but he was waiting on doing the floors, so we also had the gap between the bottom of the doors and the floor.
Now, my dads doors are made from wood, so what we did was easy for that type of door.
What we did was get two 2x8's, cut them to the same width as the doors, and drilled 6 slotted holes, about 1 inch long in them so we could screw them into the inside bottom edge of the doors. We made sure that the screws did NOT go all the way thru to the outside of the doors.
Then we attached the bottom door seals to the bottom of the 2x8's.
Because the 2x8's were the same basic thickness as the bottom of the doors, the seals fit really nice, and the slotted holes allowed us to adjust each door up and down an inch to get a perfect seal.
This worked great. When the floor was finally poured, we just took the 2x8's off, and put the seals back onto the bottom of the doors.
It was fast, easy, adjustable, removable, and worked like a charm.
Oh, and he painted the 2x8's the same color as the doors, so they were really not that noticeable when they were there.
Jim