I guess I don't know what you mean by your routine changing on Saturdays, but I think that is normal. At least if you work like I do. I have to get stuff done on the weekends so we go to the grocery store, church, outside to work on the yard, etc. Up front I will say that I have read a number of books, including Healthy Sleep Habits, Happy Child but I still am not convinced that the right thing to do it to let my daughter cry and not respond to her when she is 7 months old. I may believe it when she is older, but not yet. I have posted a couple of times about my daughter's sleep schedule and I often get "read Healthy Sleep Habits, Happy Child" though, so maybe I am off the mark. However, my mother rocked me to sleep and I am now able to fall asleep and stay asleep just fine and neither my parents or I ever remember me having a problem sleeping even when I was little.
We try to watch our daughter closely to see when she is tired. For my daughter normally she slows down and looks like she is daydreaming when she is tired. At that point we work on getting her to sleep. I cannot yet just put my daughter in her crib and have her fall asleep. We try every now and then, and sometimes it works and sometimes it doesn't, but most of the time I end up helping her fall asleep by holding her in the rocking chair.
If we are out and about on the weekends she often falls asleep in her stroller without any fussing and sometimes in her carseat. I may be deluding myself, but I don't think this is a terrible thing for her to be able to adjust and sleep while we are out and I think she enjoys being at the zoo. I try to make sure she gets one of her naps in her crib though. She just recently switched to 2 naps and I try to make sure the afternoon nap is in the crib since it tends to be a longer nap. But sometimes it doesn't work out.
I say go with the flow. If your daughter is tired try to help her fall asleep. Take her somewhere quiet and hold her, or take her for a walk in her stroller. In the long run I think the important thing is that she gets enough sleep. If she falls asleep the rest of the time fine, I don't think helping her once a week is going to hurt anything.
D.