--set-time [TIMESTAMP] is included in the CLI error message, but not in the online documentation. If this is a supported feature, it should be documented.

The command would be more useful if it used the general Meshtastic syntax --set preference PREFERENCE and had the matching -- get avaible. That way it could be used as an admin command.

By POSIX definition, TIMESTAMP should be the integer number of seconds that have elapsed since January 1, 1970, at 00:00:00 Coordinated Universal Time (UTC)

This command sequence works for me in CLI:

MDATE=$(date +%s)
...
 --set device.tzdef 'EST5EDT,M3.2.0,M11.1.0' \
 --set position.time $MDATE \

I do notice that my Heltec v3.2 with firmware 2.6.11 displays New York time as requested.
My Heltec V4 with firmware 2.7.12 prefers to display Zulu time (UTC)