apparently after 12 hours infection can set in. because ds2 wasnt born untill arround 18hours after mine broke, i copped a huge ear bashing of one midwife and both ds2 and i had to have antibiotic drips and blood tests every few hours for a few days "just to be sure" due to the time frame.
It depends on hospital policy - with DD, my group practice mw was happy to let me go to 4days as long as I took my temp every 4hours and she would come and see me 2x a day. With DS, they were giving me to the Monday morning, so that would have been 35 hours (luckily for me, L&D were really busy, otherwise it would have been 24hrs) and it was a different hospital each time. Although with DS, i was GBS positive, so had to head to hospital once my waters broke for antibiotics anyway.

With DD, contractions started 16hours after waters broke and she was born after another 16hours, but between them breaking and labour starting, I was getting uncomfortable niggles.
DS, it was 24hours without a single niggle until they started, but then it was only 4hours till he was born, (and only less than 1.5hours of active labour)