"Don't activity with achievement."
The above quote is the problem with practicing for time (like practice records that only note time spent.) Our goal in the practice room should not be activity, but achievement.
Every one of us can get more done in a super-focused 30-minute practice session than in a distracted 60-minute one. So hide the clock, write down exactly what you are trying to achieve in any given practice session, and don't get up until it's done.