I am using https://api.slack.com/methods/users.lookupByEmail Slack Web API to get user details. Does the 'updated' property in the response represent the last updated date, if so what format is it in? Or is there any other way to get last updated date of user details/profile.
Yes, updated
property in the response represent the last updated date.
It is in epoch time,
you can find more details about epoch time here:
https://www.epochconverter.com/
you can also get the same data by using users.info
api method:
https://api.slack.com/methods/users.info