I think as long as you do a thorough job warming up, once a day is fine. Even when I’m doing micro practice sessions I do a half hour session at the start of the day which includes warm ups and technique for both hands.

Another strategy would be to put easier music at the start of the practice day, warming up your hands as you progress. Or maybe doing a longer morning warm up and then running your hands under warm water for each other practice session.

One question about micro practice, something I have already explored on the CG Forum.

Which is, what about warm up? Especially if one has small hands as I do, I find I have to work a bit to get a decent stretch both up the fretboard and for the 3rd and fourth finger on the 6th and 2nd strings, same fret, very common position in CG. If I don’t warm up I don’t make it and I am afraid of forcing and injury.

One responder suggested warming up once a day is fine.

What do you think?

http://theguitarjournal.blogspot.com/2009/06/practice-log-v150.html

And I even got a specific Casio watch with preset timers!

http://theguitarjournal.blogspot.com/2009/05/watch-for-practice.html