Possible to train for a century when you can only ride 2 or 3 days a week

[ny biker]

I usually one ride twice a week, with one long ride on the weekend and one shorter ride mid-week, usually Wednesdays after work. The mid-week ride is generally only 15-18 miles long but it's hilly.

I would seriously consider a mid-week trainer workout if I could only ride outside on weekends.