Date and Time Zone in Messages

I want to cross-check the date and time a participant completed their survey using the time stamp in the data file downloaded from Qualtrics and the date and time posted to the message board. Because my participants completed the study from different parts of the world, how do I know if the completion date and time that is posted to Prolific is according to my time zone, other participants, or some other time zone specified by Prolific?

Thanks for your time.