NFL is generally no help for getting value on a freeplay there because as Ace said, it's limited to spreads. And even if it's a spread it'll cap the odds at +125. If you want to unload it on +3 -110, be my guest but that's a horrible idea. So the time of year is really totally irrelevant.
Secondly, unless you have a rep call you, you're almost never going to get more than 1k in freeplay at a time, but yes you could bet 1k or 2k in freeplay all on a SPREAD with odds < +125.
It's completely baffling to me how people will prefer a 25% cash bonus to 100% freeplay. It's like preferring 1 USD over 3 CDN because "the US dollar is better than the Cdn dollar".