Yeah, makes sense. Thanks for the response!I didn't actually test this. The goal has been to simply be able to have more than 40 icons, and that was all I focused on.
It's entirely plausible that this is indeed a side effect. Theoretically, the only length of time that the 3DS-side has been played is less than 4 seconds, so Activity Log showing only one minute makes sense, regardless of how long you've played the actual game behind it.
I think this is just one of those things you're going to have to deal with as a consequence of having more than 40.