Hopefully they have figured out a way to have good comms with the Arihant subs, so that they can launch the K4s ASAP once launches are detected. Early warning rn is dependent on radar, we need to have IR sats to detect launch plooms.They have the warheads mated and launchers stowed in hardened shelters, they roll out, fire the missiles, and get back in.
This has been the primary driver (for India) of first creating a second strike capability, second - a rapid counterforce capability (Agni-P) once missile launches are detected