What time scale is used by PTP and what is the relationship to other time scales?
PTP distributes TAI (International Atomic Time) time scale. TAI does not consider leap seconds and is currently ahead of UTC by 37 seconds. GPS distributes GPS time scale. GPS time was zero at 0h 6-Jan-1980 and does not consider leap seconds. GPS is now ahead of UTC by 18 seconds.
TAI is always ahead of GPS by 19 seconds, fixed since both time scales are monotonic.
Local time is affected by the time zone and can only be set locally, at the device which is presenting the time. Local time is typically offset +/- from UTC time.