I agree with the many comments above. The 3-4 hours sync time is an issue. If it were 30 minutes that would be acceptable, but every three to four hours? That is half a work day without tasks synced to the calendar. Or if there were a way to set the snyc schedule manually.
Maybe there is a way to do this with Flow, but I don't have a lot of extra time to play with creating flows. And I think it is reasonable for the calendar to be integrated.
I am a BI specialist, which means I work on items from every team in my Organization. So additional option to show on the calendar such as the Group name, any tags assigned to the item and the priority would be really helpful. Right now I have to make sure I put the team name in the task description so I can see that on my calendar.
Also want to say that for a fully robust use of Planner I think it also should have some way for Managers to be able to see others tasks. And a time tracking feature would round it out nicely.
But having this calendar even without a current refresh is certainly better than what I could do before with TFS tasks.