I have a bit of time to clean off the bike and a choice not to ride it when it's really messy out.
http://sprinterdellacasa.blogspot.co...your-bike.html
Ideally I clean my bike virtually every day I ride in bad conditions, usually right after the ride, and about every second-fourth day I ride outside. When I ride indoors my "bike cleaning clock" is on pause.
Last week I rode 6 times, 5 outside, and washed my bike 4 times (one day the roads were dry). If you do this consistently it takes very little time to clean everything, including your drivetrain. If you can see what color your upper derailleur pulley is before you leave for a ride, you probably have a relatively clean bike. I hate getting really dirty cleaning a neglected drivetrain and keeping the bike clean all the time prevents me from getting really dirty.
Clean drivetrains last longer and I don't want to be buying chains and cassettes unnecessarily,
cdr