My daughter made this calendar in school, similar to this one. This is an example of kagami-mochi which I talked about in this old post. As Wikipedia explains, Kagami-mochi are broken apart after Oshogatsu (Japanese New Year, January 1st), and the mochi bricks inside are consumed on the second Saturday/Sunday of January.
Happy New Year!!
P.S. This post might be early for West Coast readers, but I didn’t want to miss readers in the EU and Asia. :p