I find lunchtime and between dinner and bedtime are best for me. Lunchtime is easy for me because I work from home. If I didn't I suspect I'd make time after I woke up and before breakfast.

Concerning meditating throughout the day what works best for me is bodily sensations. I find it is basically effortless regardless what I'm doing but especially when I'm driving.

Ever notice when you're driving a large part of it is pretty much subconscious, on auto-pilot? I find it's a time where the mind is often occupied ruminating in the past or planning/anticipating the future. Have you ever experienced arriving at your destination and not remembering the last mile or so, or realizing just after passing an exit that it was the one you needed to take?