I don't have a practice schedule either. Like a lot of folks here, I suspect, I practice things as-needed. If I'm about to draw a panel that has a horse jumping, for example, and I'm not sure how to draw that, I take an hour or so to figure it out and experiment until I think I've got it well enough.
Sometimes, if I'm going to be drawing a new environment in my comic, I'll take a day or two to figure out how I'm going to draw/color all of the major features by copying some references photos as closely as I can, or doing color tests, or whatever. I did this when I had a scene set in a wheat field at sunset.
Yeah, I don't have a practice schedule. I just practice when a specific issue comes up.