Furthermore, Fox had fewer primetime hours at the launch of their primetime than that of The CW.
The CW was able to cobble up six straight nights of primetime right away (they didn't program Saturday nights until 2021) because programming-wise, it was a merger of UPN and The WB with few new shows.
Fox on the other hand, needed to take until 1992 to get that many nights on their primetime schedule, and until 1993 to have primetime seven nights a week.
Granted The CW stopped programming on Sunday nights for a time. Still, Fox had a seven-night schedule for just less than 2 years when it started broadcasting the NFL.