How long can a JRT hold it safely?

Hi, I have lived with Steve (my JRT), for about 3 years now. I am in the military, and have recently had to stay at work for over 13 hours. Steve has never gone to the bathroom inside since the first month I brought him home @8 weeks old. I usually come home everyday at lunch to let him out, but when we are in higher FPC, they will not allow anyone to come on, or leave base. Sorry for the rambling, but I am worried he might hurt himself by holding it too long. I would rather he go in the house! Will he automatically go before he can hurt himself? I ask since I have been gone for over 13 hours 3 times in the last month and he waited till I got home to go. I am searching for someone to let him out in a contingency, but I have no immediate neighbors. I am also weary of who I let take care of him (he is quite the handful)!
Sorry for the long post, just worried about my boy!