How are the cyclists in Tour De France timed ?

Question

Are the cyclists' time start/resume when they cross the starting line (with sensor on their bike)? or does every cyclists' time start/resume when starting gun is fired

Answer 1

They all start at the same time. And on the majority of the stags, most of the finish at the same time too. If you're in the main peleton, you basically get the same time as everyone else.

Answer 2

Time starts for everybody when gun is fired.

Total time is electronically taken at finish.  As groups cross the line. all riders in group are given that time.

In case of a crash, If it is in the last 3 km of a flat stage, those involved in the crash are given the same time as the group they were in at the time of the crash.