@property<EOL><INDENT>def start(self):<DEDENT>
try:<EOL><INDENT>return datetime.datetime.utcfromtimestamp(self.timestamps['<STR_LIT:start>'] / <NUM_LIT:1000>)<EOL><DEDENT>except KeyError:<EOL><INDENT>return None<EOL><DEDENT>
Optional[:class:`datetime.datetime`]: When the user started doing this activity in UTC, if applicable.