Once your competition robot is operational drive practice is something you should aim to do as often as you can, while keeping in mind the physical limitations and wear and tear that may occur. However, choosing to sacrifice time for drive practice for other tasks (Fine-tuning, programming autonomous, etc.) is something that is dependent upon where you're at in the season and a decision you'll have to make for yourself.
Drive practice doesn't have to be treated as completely separate from build though, it allows you to see which areas of your robot may need improvement and can give you a better understanding of what your robot is capable of. This coupled with iteration on these flaws will make you much more prepared for your competition, and you should see a drastic improvement in your performance.
During drive practice I'd recommend setting a time limit of 2 minutes and 15 seconds (Standard teleop match time) for each round, this will give you a good understanding of how long that truly is and what your robot can accomplish in that time.
There're plenty of good resources on this (and strategy in general), I'm sure you can find a few threads on this topic. The first one that pops into my mind is
1114's notes on strategy.
When a team is a team, anything is possible - Bharat Nain [more] 
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