I do these in the 20-25 minute range with my phone out filling in some of the form as I go. I then finish it in the car before the next store. I get into a rhythm with the shops doing the walking around count and then hitting the departments. Remember if no one is there after two stops (for the most part) you are then done. No need to wait around.
I as well love to grocery shop and have done many...my trick is to take a list of what you need, get it, do whatever you need and get out...this takes me 30 minutes, unless I feel like browsing, but I go at the time they start when it's not that busy, time is important, and am out...haven't been doing as many as normal as we have new shoppers here, and I'm eating out so much, not to my advantage as I always spend more...still it's been a great way to supplement my income and get gourmet food.
For me how long it takes depends entirely on which store it is. The one closest to me, I can do in about 30 minutes because it's small and I know where everything is. The next store size up I can do in about 45 minutes if I've been in there a few times. The super sized stores take closer to an hour. Most of the time I spend for all of these is because of the counts. The 2 biggest ones I've been in (one had a beer bar?!!!) took me more than an hour.