Can I Schedule Some Hours With No Slow Songs At All?
Yes, you can do it by entering zero in the Tempo "hours" box on Clock Rules.
BE CAREFUL WITH THIS: If you rule out slow songs in a clock and you use that clock many hours of the day, you probably will soon have other hours scheduled with too many Slow songs. You see, one of the primary directives of M1 is that all songs in a category get the same number of spins. So, if some hours omit slow songs, those slow songs still have to be scheduled somewhere; they have to get the same number of plays within the category as all of the Fast and Medium songs in that category.
Unless your library is over-balanced with many, many more fast songs than slow songs, a clock rule such as this could quickly lead to a lot of stops" during scheduling when M1 gets backed-up with many 'must be scheduled' Slow songs.
There are a couple of ways to handle this better. One, you can create "tempo'd" Categories. Like, Gold A (with all fast and medium tempo songs) and Gold B (with all slow songs). Recurrent A and Recurrent B built in the same way, and so on. Then you can create clocks using only the A Rotation categories.
In Version 7/Professional, there are "selection" categories that allow songs to be in two categories at the same time. Using those, you could do something similar to the above, making tempo'd Categories for use in your special hours, but using the 'regular' categories that have the full mix of all tempos in most all of the other hours during the week.