If you have a family, time IS a factor.
As such, I have run a lot of experiments with mash time. For me and my system, the limiting factor was attenuation. 20 minutes wasn't ever long enough for proper attenuation, e.g., the final gravity would quit at like 1.028 and be done. 30 minutes was enough about 50% of the time. But 40 minutes always works, so that's what I do now -- 40 to 45 minutes. Try it and see. No need to mash for 90 minutes unless you want your beer to be as dry as possible -- heck, then why not mash for 2 hours or overnight if you want it that dry. But for 95% of styles, 40 minutes is perfect. At least for me.