I want to add clock to display call duration. Is this feature available in Jitsi-meet or how I can implement it using any existing properties.
This feature is not currently available, but I say it is interesting one.
To implement it, I see it this way:
As jicofo is the one that is available in the room from the beginning till the end of the conference, this is the place to store the start of the conference. Every client when joining send an iq to jicofo and there in the result you can return the start of the conference in a timezone independent timesestamp, then this will be handled in lib-jitsi-meet and exposed so jitsi-meet can retrieve it and show it, clients can be in different timezones than jicofo.
This approach will have problems if the client machines does not have a correct time configured, so this can be extended in such way that with the initial iq clients can send their timestamp and jicofo can calculate based on that the beginning of the conference and send as result this value so clients can calculate the beginning of the conference based on their own clock.
Mobile App: When conference started