I agree with the other posts recommending you talk to HR generically about what the options are. Perhaps they simply have no policy to support your request and therefore going to your boss would be pointless.
I work with a woman who for no other reason than "it is nice to have an extra hour in the morning and an extra hour in the afternoon and every Friday off just to get errands, appointments, homework, and housework done." She has no medical need whatsoever, but she asked and agreed to certain conditions (her salary and benefits and time off are *significantly* pro-rated) and it works for her.
I had another friend that asked for a custom/lighter schedule and her employer said, "Sure thing! No problem." Then she was excluded from projects, not eligible for trips or educational opportunities, promotions, and was the first to get laid off when the economy turned. And this upset her. But my thought was, she needed the job for money and benefits and except for those things, she wasn't passionate about it at all. She took herself out of the race to dedicate time to her kids and wanted to "have her cake and eat it too." She wanted to get a promotion over a woman putting in 50 hours a week, doing things that weren't her job, working on her MBA, etc.
I just tell that last story to make sure you understand and are comfortable being in the slow lane at work while your colleagues move ahead. If you are -- Then give it a shot.