I found POSIX time entry field in xephem to work with UTC offset 0: the mount then does not show Zone 2 (offset 2) like before, but it correctly show UTC with no zone (GMT time).
Hope this "addendum" not to be considered an --off topic-- discussion here,
I found in the past during "mount learning" often 1 or 2 hours unespected displacements while pointing to an object with the mount , that anyway needs an alignement procedure based current time and site, to correctly translate RA/DEC into mechanics.
Indi CelestronGPS foresees an UTC offset in a separate entry vs UTC time entry, that (myself ...) did succesfully think .. OK, it is as POSIX time format..,.
These fields should be better documented.