Very large (almost 4,000 students) state school here.
Book as many appointments as you like, online booking system
5 minutes long, you must leave a 5 minute slot between each appointment to walk to the next one
In person
Range of times available - on appointment day, school closes at about 1.30pm or 2.00pm (instead of usual 3.20pm) for appointments to start, so you can book anytime from then up to about 8.00pm or whatever time it finishes (although not all teachers may be there for the whole time and they do get breaks)
Judging by numbers of parents there on appointment night and the appointments that are available, it appears that many parents do not attend, presumably because they don’t see value in it (and this is a school where parents generally are interested in their child’s education, people go to great lengths to get into this school). I personally attended the first year my daughter was at the school, and then seeing no point to it, only booked three appointments the following year. You can’t talk about anything in depth in 5 minutes and they only give positive feedback.
We’re in NZ so only just starting our school year now, I’m not sure if I will bother attending this year or not. Teachers are generally responsive to emails so I would just email if I had any particular issues instead of waiting for appointment night.