I'm not sure how this would be implemented. Do you mean that the current Smart Lists should automatically apply a filter based on the day or time? To use tags, the tags would have to exist already, but I wouldn't want RTM to force those tags on me if I don't want them. Also, if the filter is part of RTM, then tags wouldn't be necessary, right?

Anyway, this idea can be done with multiple Smart Lists already:

Weekend: list:{mainList} AND tag:weekend
Evening: list:{mainList} AND tag:evening