You can certainly ask about work life balance when you interview. You can also ask about the tele-commute policy.
I always look at the senior leadership team and ask myself "how many of them take advantage of a flex time policy?"...if the answer is none, then I would stop and really consider whether or not I would partake.
Before asking your manager, I would consider if your work could be done from home. Are there any privacy issues? What would be the impact to those not working from home?
If you continue to feel that there is an unwritten expectation regarding the flex-time, then sit down with your supervisor and talk about expectations and your performance.
Although companies are becoming more open to working remotely, there should be a reason for requesting to work remotely on a regular schedule (ex. child care, transportation issues, etc,). I would not recommend approaching your manager with such a request unless you have such a justification.
Managers and organizations usually care less and less about when, how and where you get your work done after you have proven that you will get it done and completed with quality.