We are all different - some people find they need 24 hours for the sensor to settle down. some people find they need 48 hours and some people find they need no time at all.
The only way to find out what your body needs is to try it.
I need 48 hours for my sensor to bed in. But if a sensor fails before I have had a chance to bed in a new one, I will apply a new sensor and then activate it straight away but test with finger pricks more often for the first couple of days.