The current ‘idigi/Dia’ design is to use the real-time clock from the X4. The code doesn’t care if it is UTC or localtime - it is just ‘the time’.
There is no way to allow the X4 to hold UTC but upload in ‘local time’.
However if you manually manage the time withing the X4 (don’t use cell time, nor STNP), then nothing stops you from putting local time into the X4 realtime clock, which then will be uploaded to iDigi.
The logic is that managing localtime with seasonal adjustments (day-light-savings, etc) is too complex for such a simple product.