NICE guidlines say they should offer you monitoring for up to 96 hours before offering induction but most hospitals I know gently insist on induction after about 48 hours.
My waters went early Wednesday morning and I was told I would have to be induced on the Friday evening because of the risk of infection. At the time I didn't know about NICE guidelines and I wish I'd held off and waited to see if he came naturally because I really would have liked to use the birthing pool.