https://www.epo.org/en/node/conduct-oral-proceedings-1

Can I leave my microphone on the whole time? There is often a delay when switching it back on.

The chair will decide how to conduct the oral proceedings but, in order to avoid background noise, the microphones of all participants other than the chair should normally be muted.

The parties and members of the division other than the chair should switch on their microphones when they are given the floor by the chair. Delays in activation of the microphone will be taken into account.