As explained in Piro's rant, あいだに。。。 = Aidani... = Meanwhile...
Piro's rant also explains the vertical four panel format.

Piro speaks:
Just a quick comment on the 4 koma thing. It's one of those 'it has lots of advantages' kind of things, and the way the stories are coming together, and the way MT works in general i'm working with this concept in relation to the real life way i put strips together.
Sometimes you guys get stuck with SGD strips or DPD days more because i dont have time to do a regular strip. there are times when there just isn't that 8 hr block of time. 4 koma strips are easier to make, require less drawings, and are easier to refine - and oddly enough, simple humor can be very nice. 4 koma strips are meant to be an 'intermediary' step between SGD DPD and full blown strips.
Now, that said, they are, actually, fairly planned. But the nature of a 'meanwhile' strip is that the next one could be next week, 2 weeks away, 3 weeks, whenever - the placement of them can be somewhat flexible, becuase they are side steps from the main story arc. I had a very busy week this week, so two 4 koma strips worked well. Also note that i will tend to do them in pairs, because if i ever go to print with these, i want to be able to stick them together on a page.
The events in 4 koma strips are part of the story. Heck, even the DPDs have some impact on the story, its all intertwined, and its all just part of me experimenting with ways to keep things going smoothly while dealing with my slow ass way of doing things