It all depends on hospital policy. With my daughter--I had to stay for 48 hours after birth so they could monitor the baby for possible infection. I did have the antibiotics, though. So I'm not sure what the policy is without.
With this pregnancy I'm with a different hospital. I have GBS again. They only require you to stay 24 hours after the birth (but I'm opting to stay the full 48 hours to rest). But, again, I'm going to have the anitbiotics.
I think that if you don't have the antibiotics they will insist on longer observation of the baby. I don't know. It's a tough one. You could also request another test at your next appointment to see if the infection has cleared. It typically only lasts 4 weeks. So, it's possible.