How to set time limit for a SharePoint Calendar?

Just found this thread. I was looking for the same thing and I came up with a solution. Go to the calendar you want to set up the time limit for, click on Calendar in the ribbon at the top, then click on List Settings.  In the General Settings, there is an option called Validation settings. Click on that. You'll need to put in a formula to check to make sure that the time doesn't exceed four hours. Here is what I put in: 

=AND((([End Time]-[Start Time])*24)<=4)

Then, in the User Message, you'll need to put in a message alerting that the time is longer than allowed. This formula works great for me. Hope you can get it to work.

EDIT: It's not perfect because for some reason, trying to schedule from 10:00 am until 2 pm returns an error message but if I switch the time from 10:00 am until 1:55 pm, that works. This error also happens from 1 pm until 5 pm and a few other times. I haven't figured out why, yet.