Was the Daytona 500 ever postponed?

The first Daytona 500 was on Febuary 22, 1959. And NASCAR has been established before the start of the Daytona 500, so the answer your question...no.

No, it was not. For example, for most of the time that NASCAR raced there, the now gone, Riverside International Raceway (CA), a road course was the first race of the season.

There was no "Daytona 500" until the speedway was built in 1959. Even before that, the races on the beach at Daytona were not the first race of the season.