It depends on the BMS's lvc, a 36v battery though can generally be taken down to 30 - 33v . When I buy or build a new battery I always take it down to lvc once just to know the lowest cut out voltage in use, the voltage usually rebounds a little higher as well .
Typically though there is little point in going much lower then 35v or 36v if riding locally , the extra capacity below 35/36v comes in handy as reserve for longer rides if a spare battery isn't used.
37.5v - 38.5v (storage voltage) is a good voltage to leave the battery at if not being used for a while.