From my experience I can say that I have stayed in various monasteries as a visitor, and have also done some retreats. Both with strict and with loose schedules.
Bhante Sujato for example emphasizes that for the upcoming retreat we are organizing with him in Belgium “all sessions are optional”, and Ajahn Brahmali who came to teach a retreat for us two years ago said in his introductory retreat instruction, “there are only two mandatory sessions during a day, that’s breakfast and lunch”. That is certainly a bit contrasting to what you may have experienced in strict Vipassana retreats.
Likewise I found it in monasteries. Some have a very strict schedule with regular group sittings, others leave it more or less to the individual how to structure your day. As people are different, this is good. Personally I find it more conducive with a loose schedule.
Unlike in many retreats, in a monastery there is usually a work period during the day, mostly in the morning, which involves preparing the meal and other works depending on what is needed. A visitor is expected to participate in these works according to their capacities.
But this also varies much from one monastery to the other, also depending on the time of the year. I have spent a Vassa period in Bodhinyana in Western Australia. They have certain duties for female visitors I had to share with one companion. We divided the duties week-wise, so each was “on duty” for two weeks while the other one was on a self-retreat. On each Uposatha day we would switch. This was a very nice way to spend the three months!
I might still add that staying in monasteries has taught me not only how to meditate which is the main purpose in most retreats, but it has given me a deeper sense of what it means to live a Dhamma oriented lifestyle. It is like diving into the Dhamma more deeply and more wholly, if I may put it like this. This came also across to a certain degree in some retreats, especially the more loose-scheduled ones I have been participating in, not so much in a strict Vipassana retreat.