While I understand that it's frustrating if you want to crit a mun that's not available, I've... never really seen it as an issue in Kiseki? Maybe I'm missing something. It's always seemed to me that 99% of the game participates regularly, and when someone doesn't it's almost always because they either are on hiatus or just came off an extensive hiatus that's kept them away from the game for most of the month.
Of course, if the lack of activity is something you'd want to crit, I can see why that'd be an issue, too.