As mentioned above, for many reasons every fish may not spawn every year and females will re-adsorb the energy invested in those eggs and save it for next year. This takes awhile and you can still see egg sacs in catfish well into summer.
However, with respect to eating the eggs, I used to manage a four thousand acre fish farm that processed 150,000 pounds of catfish a day on site. According to the Norwegian buyers, the eggs were at their peak in early spring for harvesting and processing into caviar. After that the quality deteriorates. The eggs are edible and nutritious, but I've never eaten any personally. I have eaten caviar from sturgeon, preserved salmon eggs, some kind of saltwater fish eggs on sushi, and white bass eggs fried with hen's eggs. Not averse to 'em, just never tried some types.
Blue catfish egg sacs tend to be much larger than channel catfish egg sacs but the eggs themselves are much smaller. A ten pound blue catfish is barely mature but you can find eggs in channel catfish that around a pound and a half.
In the lakes set up for it the blue catfish will start spawning in water as cool as the low sixties and continue until temps are well into the eighties. Channel catfish tend to start in the mid seventies, later in the spring than the blues. I took a blue cat spawn once that weighed over 25 pounds and hatched over half a million fry from it. It took two full incubators to hold it. An incubator typically holds about eight channel cat spawns.
One of the best fish on the planet, blue catfish.