Aside from spending about 30 minutes to an hour the first time to set up your player(s), it takes about 2-3 minutes every other day to check in and see if you need to do anything. The time commitment is as minimal as you want to make it...unless you own a team, then it's about 2-3 minutes every day.
I agree that it's a fun way to pass the offseason. By the way, I own the Dublin Dragons and I'm always looking for human-controlled players (not cpu-controlled players). If you sign up using BHud's referral link but still need a team, let me know.
Goal Line Blitz is a lot of ******* fun. It takes up about 7 minutes of your time a week, you get to develop players, and teams, stadiums, etc. Definitely a good off season distraction.
I play on a team that just got started this season, with a lot of folks from a couple fantasy football leagues. Once you're set up, you check in for about 1-2 minutes a day. Update your training, check the last game results, maybe adjust your tactics for the upcoming game.