What is the right balance of training and time off?

As with all things sir, it depends.
Are you trying to induce a combat-like situation with the stressors of long hours and reduced sleep? Then by all means, do so. Just make sure you take care of them by giving them a nice three or four day pass on the back end to recharge.
Are you just dealing with day to day grind? Then let them have their weekends unless it becomes necessary for them to work.

This is a very tough question to answer based on so many different established and unforeseen reasons. Since you have to accomplish all Commanders Intent(s) and any blind siding taskers, the only thing one can do is do the best you can and make it work as best you can.

To follow up, I want the question to expand into how do we get the most effective training? Is it really necessary to stay in the field for a week-two weeks at a time when you are back here in the states? Is there ways to get more effective work done so that when in garrison soldiers can focus on personal life as well? Whats the balance?! How can we be kick ass and ensure that everyone's home life is getting the attention it needs.