I don't see why this is marked difficult. If you really want the gamerscore, but can't stand the game... just start a new garden and let it sit while you do other things. This cheevo is from cumulative time across all gardens, so you'll just need to finish up whatever is left over from when you actually played it.
If you want to check your current time, go to Journal-->Player Awards-->Player Status and look at the "Game time Elapsed". Divide the number of days by five, and you've got the number of hours you've played.
1 Game Day = 12 Mins IRL 5 Game Days = 1 Hour IRL 250 Game Days = 50 Hours IRL