I wonder if there is any data on whether questions receive more attention in some months, while less in some others. Is it better to ask during Christmas or the summer break, at the beginning or at the end of the semester?

Maybe on-topic tag could be created on meta and made a synonym of allowed-questions. I think that it is quite probable that users asking about question which are on topic might look for a tag with a similar name. Several metas in SE network have a tag called (on-topic).