We had a system where visitors were required to go to a separate visitors lounge first, and phone in to the unit to ask if they could visit. The clerk would then ask the nurse "can you have visitors in bed 8?", and tell them they could come in.
We just moved into a newly constructed building. Our new unit is locked, and there is a buzz-code to unlock the door to let visitors in. There is also a cc-tv camera so we can see them. So they buzz in, ask if they can visit mr Smith, and the clerk calls out "can you have visitors?" Now, no one gets in unless they are buzzed in.
The old unit, we had a problem with people who just didn't know, and we were always explaining "you have to call in first...". Some families just would not "get it".
Visitors are generally two at a time (we make exceptions, depending on the pt, family, and how busy/critical the unit is).
No visitors between 7:30-8:30, am and pm - change of shift report, and then the oncoming nurse does assessment. It violates confidentiality, etc, to have visitors there.
Visitors are asked to leave during "rounds", which happens at the bedside and can take quite a few minutes. They are also not allowed in if Rounds is happening on nearby patients, also due to confidentiality.
We ask visitors to leave during care activities such as turns, dressings, x-rays, etc.
Because it is done uniformly and it's just matter-of-fact from the staff, every family goes along with it. Other than these times, we have 24-hour visiting, but encourage families to go home and rest for the night.
(PS I work in SICU, but the MICU does the exact same thing)