Well, it depends! To play it safe, you may want to let managers only share the written feedback after the meeting. This way you prevent unwanted circumstances, for example if a manager writes harsher feedback than she means to, and the employee gets upset or scared the day before the meeting.
On the other hand, once managers have some experience writing reviews, it may be fairer to provide the feedback before the meeting so the employee can prepare accordingly. If you want to share before, we'd recommend sharing it an hour or two before the meeting, but not the day before. This prevents a misunderstanding from turning into a big issue and a sleepless night. If there's misunderstanding, it will be resolved at most 2 hours later.