Parents... Encourage and help young players set up and keep this routine. Schedule around this practice time. Don't bump it or move it. Daily practice is essential for steady progress.
Kids... Would you skip football practice? Would you skip soccer practice? Would you skip swim practice? Gymnastics? Basketball? If not, why would you skip guitar practice? You wouldn't let your team down; don't let yourself down.
Adults... Don't answer the phone. Don't go get the mail. Don't check email. This is time you scheduled for yourself.
Breaks... Every half hour or so for those who practice a lot.
Six... days a week is great. Seven might be too much.
Mark's detailed practice tips are listed here: www.bigtimemusic.org/practice.html