I couldn't find the exact chapter that mentioned this... but I did find this page

http://manga.redhawkscans.com/?manga...&page=4#page=3

The three festivals pass with one week between them. We already had the sports festival (with Keima running with Chihiro). And the 2nd festival... actually the mid-terms... happened the day Kanon was stabbed.

Since 4 days have passed since that day...