To maintain a good relationship, it’s of course best to be considerate and respectful of an SAs or clients time. When I ask my local SA for an appt, I indicate kind of what I’m interested in, or DH is interested in, or both.
We rarely come in with a list, and we like to rummage around and be surprised. But, our SA tends to pull stuff that she thinks we would like. So, they block however much time they think we need. We’ve never been rushed, but to be polite, I always check if they are crunched for time. Sometimes they run late with someone else, but that’s not a big deal. I wait on the couch or browse by myself and/or chat with the SM etc.
I’ve rarely if ever shopped in an hour or less, bc there is so much to see and try on.
Sometimes, if I text last minute that I am in the area and want something, of course, I understand that they may be busy and I don’t want to take up too much time. In that situation, they do me a favor if they can squeeze me in. I’ve never shared time with another client though. At FSH, at the start of the appt, my CdC assures us that I have all morning going into early afternoon (so I think they do book 2-3 hours). Mine shops with us throughout the store, including leather. She does bring in a sweet SA who helps with men’s RTW, who we know from prior visits. So it’s kind of like a mini reunion. An SA, either local or abroad, also needs time to hunt up items, check sizes, run around, so it’s best not to rush. *
ETA: I prefer an appt, first thing in the AM on a weekday, but on some days midweek, it’s more convenient for me to go early afternoon. For the latter time, it is a lot more busy, and understandably my SAs and I don’t take as much time together.
I also love to hang out with
@haute okole and her SA. He is clear on booking two or more hours with her (I’m just a bystander), and it’s nice to chat and relax first

That is their special rhythm. Everyone is different.
*ETA: my FSH CdC comments that she sees some appts every month. She said of course she makes sure to book more time with those of us who she only sees twice a year.