My guess would be that NADIR passes, when the satellite is directly overhead of the target, would be around 7 minutes, but OFF-NADIR passes, when the satellite passes out on the horizon, would be less than 7 minutes. To visualize, draw a circle, then draw a line through the middle of the circle, and draw a line out closer to the edge of the circle. You can see that the line on the edge of the circle is shorter.
Unless you’re only going to use the NADIR passes, which lessens your passes per day, the software will need to be able to handle data increments as low as about 2 minutes.
If you run sun synchronous to keep your solar cells powered, you’ll get two NADIR passes per day per satellite, and 8 off NADIR passes per day per satellite. (One off by a single pass and one off by 2 passes both to the east and west). As a rough guess, that would mean:
72 + 44 + 4*2 = 14+16+8 = 38 minutes per day per satellite
$.02.
