Wednesdays are my preferred days for team-wide meetings like demos, sprint planning, and retro. The reasoning is that holidays often fall on Monday, and Friday is a common vacation day. So if you have meetings on Mondays or Fridays, you’ll frequently need to readjust the calendar invitations, and often a good portion of the team will be absent.
Another benefit is that if sprint transition is on Wednesday, people might put in the extra effort to complete their sprint goal on Tuesday. Whereas if the transition is Monday… people tend to not push their efforts on Friday. And we don’t want people to feel obligated to work over the weekend.
Tuesdays and Thursdays are also good days for meetings, but Wednesday is right in the middle, so why not?