Wouldn't it really depend upon the constraint, as in why? If it were for some reason like being in a situation of limited or no privacy such as military basic training then I could (and did) go as long as necessary. Otherwise just living my life, why deny myself that basic pleasure?!
While my GF is out of town I'll indulge more than once a day. However, when I know when she's coming back, I'll refrain for a day or two, so that I'll have an extra large load for her when she does get here.