Timestamp synchronization feature has been introduced with firmware version >= 0300.
The hardware clock is disciplined to the host's system time, to prevent clock drifting.
The feature is always enabled on Profishark 100M (blue), 1Gv5 and 1Gv6. To enable it on 1G+, the timestamp initialization must be set on "Initialize from system time" and "Synchronize timestamp (experimental)" must be enabled.
When the feature is activated, the Power LED blinks in sequence with the time counter (off: odd seconds, on: even seconds).