I've gone all times of the year; I honestly didn't notice a lot more pressure on opening weekend compared to the 2nd-3rd weeks when we used to go. If someone is in a spot just go somewhere else, it really isn't all that complicated. If a field has good habitat and there are crops nearby there will probably be birds there. Save your best spots for late in the day, but I've filled many limits from 10-12 without any corn being harvested yet, there are still plenty of birds loafing in the grass mid-day.
If you can figure out taking work off, I personally love the late season as well. I always go in early January, sometimes the hunting can be tough, but when it all comes together you can find pockets of birds and the hunting can be great. I also rarely see another boot track that time of year.