I have had conversations with several young men on how to strike a healthy balance between work and family. These young men, all of them engineers, find that their work schedule tends to expand and crowd out the time that their families deserve. I have offered them two defensive strategies to protect family time.
The primary defense I suggest to a young engineer is for him to take ownership of his schedule. This requires him to plan out a detailed, day-by-day work schedule for the coming three weeks or so. This schedule should be sane and have enough margin so that family time will not automatically be sacrificed if any of the usual office mishaps or snags pop up. This schedule should then be updated each week. As part of the scheduling process, it is good for the engineer to discuss this planning with his wife and agree upon goals for family time during the coming three weeks. (These discussions generally help to reduce wifely surprise and aggravation and the resultant nagging.)
Some engineers, whether from timidity or laziness, passively wait for their boss to hand them a schedule instead of actively influencing the scheduling process. This is a mistake. A good engineer should be a problem solver, not a lackey. The first step to solving a problem is to define the problem properly. The engineer needs to define his schedule problem in terms of getting the work done while still protecting family time.
Once the engineer has created his three-week schedule, he needs to explain/sell this schedule to his boss. If the detailed schedule is reasonable and supports the overall project schedule's delivery milestones, his boss will usually concur. After all, his boss has plenty of headaches of his/her own and will likely be grateful that the engineer is taking responsibility for planning his own work. The boss's concurrence yields the happy result that the detailed schedule now becomes the basis for the boss's expectations. If snags arise, the detailed schedule gives the engineer a credible way to quantify consequences and propose mitigation (e.g., adding manpower, reducing scope of the effort, or using some of the schedule margin held by management to avoid a day for day slip of the final delivery date). In the absence of a detailed schedule, there is less accountability. A boss could insist on keeping the final delivery date fixed and expect the engineer to donate his free hours (family time) to overcome the snag. This is often expressed in the tiresome words: "You're a professional. We expect you to do what it takes to get your work done."
The detailed schedule is not a perfect defense. There are sometimes legitimate crisis situations that call for extraordinary effort: viz., urgent proposal writing to capture new business, meeting the final deadline for a system delivery, and responding to major calamities. These crisis situations are typically short and intense, a matter of several exhausting weeks. The engineer ought to do what is necessary to deal with the crisis. However, if an engineer finds himself continually working in crisis mode, it is a clear sign of management incompetence or an industry in trouble. (I worked in perpetual crisis mode right before the synthetic fuels industry collapsed in the 1980s. My copious amounts of donated time profited me nothing.)
The second defensive strategy to protect family time is to inform your boss of family plans and obligations ahead of time, such as: "I'm taking the family on a boat trip next weekend." The idea is to define a discrete period of family time and remove it from consideration as open time that work can spill into. Most bosses will hesitate to ask you to work extra hours if it means explicitly telling you to cancel your plans.
All in all, the key to life balance is valuing family time enough to intentionally preserve room for it as you arrange your work schedule. Scheduling becomes a bit more difficult but the rewards are great.