Kinda depends on the situation. If I'm playing in a band I'll go over the sets by myself a few times a day & practice the most difficult parts till they get easy.
If I'm recording in the studio I'll practice the songs I'm doing and listen to a recording of myself to tighten em up, get rid of noise, improve em, make em smoother...whatever they need.. plus get things to the point where you rarely make mistakes cause studio time is expensive. If I'm at home bummin around doing nothing, I'll play my fav songs, go over my 'show off' pieces or just play around & see if there's something new I can come up with. As far as a rigid schedule though, I couldn't handle it. I just let guilt or boredom or whatever that little buzzing in my brain is that says "...gotta get up and practice that thing..." and continue on like that till I don't get that feeling anymore.