You can use the Current Time attribute to limit when certain rules match. Note that Hazel will still be checking things and such around the clock. Not knowing why you need this I can't say whether this is what you need.
I want to use this app to rename and convert my downloaded series, if it works all day my computer has the fans at high speed and it annoys me I wish that only work for example between 1 and 4 a.m when I am sleeping