Hands in the air on this one as I may also have it wrong.
CG work on UTC and all distress relays are such.
We use a lot of Ray 435 conected to Icom 601s and the set up is simple and great. When first connected the Icom will show UTC time and can be simply reset by a time adjust on the menu screen.
JohnB may correct me here but my understanding is that on a DSC Mayday the time transmit will be UTC whatever the user time offset on the panel.
Do think though that whatever the case the prime importance will be lat/long and distress. Those receiving will receive at the time when it gets through unless of course we have a time warp !!