This is a pretty hard question to gauge because it varies from ride to ride.

Easy recovery rides - almost never in the drops.
Fast flat rides alone - most of the time, except for warm up and cool down which can be 30% of the ride.
Fast flat rides with a group - 100% of the time I am in front, maybe 60% of the time while I'm drafting again the warm up/cool down is the exception.
Hard hilly rides - 100% in the drops on descents, almost 0% on ascents, and about the same as flat rides on the flats.

I answered 21-50% in the poll, but after writing it out I think it may be <20%.