If you're OK with finishing rather than competing...then you don't need to bike much. I'm utterly cr*p at cycling (yes, even worse than my running)....and came lastish in the triathlons I did before knees decided to give up.
Probably cycled once or twice a month (yes I know, but it made my knees grumble)
But in a pool based triathlon they usually put the slow-ones in first, so I was never last out on the course....the speedy types were only setting off as I finished.
Good fun even on next to no training!