I did them in the past. Depending on the location it's actually not too bad. I had two locations, and I bounced between them every other month. Location A on month 1, location B on month 2, Location A on month 3, etc...
One location was very small, and I could actually do it in a day if I wanted to. The other was a big location and needed the two days.
I emailed GFK regarding the small location, and they didn't realize that Best Buy had small locations! They said I had to do it in two days, but they would still pay me for the full amount, and to basically chill in the break room.