It's basically not worth doing speed work with that limitation, so I've ended up doing about 35-40 min per day with a longer run on a Sunday. For a while every run was somewhere between 7:20 and 7:40 per mile, although I've got a bit more variation in now.
Sunday I did 8 miles at 7:15 per mile; felt tired Monday and did 4 at about 8:15, then back on Wednesday with a hilly 5.5 at 7:18. At the sharp end I do 4 min in very close to 7:00. Much over 8:00 feels pretty crappy biomechanically, as I've never got used to much really steady running - when I was younger I was a track guy doing 40-50 per week with three track session or two and race in the season, but 'steady' runs were generally in the 6:00 range.
Most of the running is on road, but I've always done that, so perhaps I'm acclimatized to it. Every couple of weeks I make the Sunday run 60-70 min on trails for variety.
Not sure what the physiological effects of constantly training at steady state/lt type paces or a bit faster are, but I do seem to be getting fitter (that is the average fast/steady is getting faster). At least it burns some calories, and stops fitness completely disappearing!