In my current save it's taken 4 months to play 7 seasons, so I guess that's about 2-3 weeks per year. I'm with the crowd that likes to watch matches, tinker with tactics, and spend a lot of time scouting.
It takes me about 48 hours all in usually spread over a week. I find it usually depends on he league system you play in also, Say if you play in the nPower Championship where you play like 48 or 46 games? it'll take longer, especially with a cup run.
first few seasons i tend to play them, and takes around 3-4 days to finish 1 season. As years pass and im building my team, i tend to skip half of the matches and i play only european games and derbies in the league.