From a recently published US study using set-top boxes:

“85% of households watch prime-time TV every night, on average watching 88% of the prime-time hours. Thus, any gains from targeting largely arise from what a viewer watches rather than whether they watch. Once a viewing session commences, 30% of households sample multiple shows before selecting one to view, suggesting that show sampling is informative about viewing preferences. Once a show is selected, 60% of viewers watch a show to its conclusion, indicating ad exposure is common once a show is selected. Within a show, we find that viewers’ advertising avoidance is more common when the show is recorded (79% [when recorded] vs 15% [when not recorded]).

from Deng, Y.  & Mela, C. “TV Viewing and Advertising Targeting” Journal of Marketing Research 2018.

• the text in [ ] brackets I added for clarity.