IME, SAHMs with up to 3 kids are less concerned with being on time. Now, all the SAHPs who I know that 4+ kids are super about keeping to the schedule, and while they might be about 5 minutes later than they expected due to traffic or something else, that usually means that they're on time, since they all build in at least 10 minutes extra to deal with the kids.
I won't work with a SAHP that has 1-3 kids unless there are twins or triplets, as the few times I've interviewed, it was obvious they wouldn't respect that I am an adult and that I am applying to help with kids, not be the housekeeper and do occasional date nights. Any SAHPs with 4+ kids have wanted minimal housework and more focus on helping keep the kids on schedule, which is fine with me.