It totally depends on the brand. I will preface my response by stating that I rarely do stations that I don't already know what condition they will be in (I am fortunate to have done this long enough that I know which locations won't have issues so take me longer) and in my area all of a specific brand tend to be clustered together so I can get in a rhythm so I don't waste time thinking about the requirements. YMMV depending on time of year as well. Interestingly enough, I can do more in the evening because there are fewer customers to work around and I actually can get more done per hour in the colder months because I move faster to limit my time outside.
I can do 10 of the Blue Stations (I just found out that more than 11 per day and then only rarely will put you on the client's radar and leave you open to being pulled off of that project. It's actually less of an issue to ask for an extension, particularly if you offer to do the assignments as evening in exchange if that time period is needed). I have done up to 12 of the Yellow Stations and up to 15 of the Green Stations in the same day. I find the Yellow ones take me longer because there are only so many ways to say the station was clean, in good repair, and the employee did their job. In my area the brands tend to be clumped together so my driving time between stations is much more limited. I also have found that the station number restriction only is brand specific (and only to the blue brand) so I can slot in other brands to maximize my earnings.
I also find that I can do more if I can use the app because that insures that I won't forget a picture. In my experience, the editors, particularly on the yellow shops, don't tend to ask for extra pictures if you submit it on the app - maybe because they know that there is only space for 2 pictures whereas if you do it through their website there is unlimited space. The largest station that I've ever done is 25 pumps (the MSC didn't even have space in their report for that many pumps!), most are around 8 pumps although the yellow brand tends to be more likely to have 10-12 pumps. My typical time on-site is 20 minutes at a normal pace, 25 minutes if I'm not pressed for time, and recently I've been averaging around 15 minutes.