User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-3965848-20150701194229/@comment-16281343-20150702045923

Time doesn't move fast in DxD especially in the recent Volumes. Events in a Volume span in a matter of days. There are no indication that they've entered March. They've just started the third trimester.

And just so you know, the third semester normally is from early January to late March; a new school year normally starts on April. Issei's birthday is on April 16. So, you're saying all those things in between have already happened i.e the whole third trimester, graduation, etc?