Im not allowed use store bathroom i work at

So I work at this place but the window washer cleans in the morning. Much of staff get there between 7am-9pm. Everyone is forbid from touching the bathroom till after 9pm. They already left in a huff one morning becuase I had switch my shirt. Do you think owner would give me permission to clock in run across the street next door if I need the bathroom. I kind of just started not using the bathroom till end of shift becuase I dont want to make this escalate to piont of losing my job. My shift ends at 1noon. Also I have digestive issues so I kind of always in the bathroom as it is.