However, the simplest method may be to go to the AO3's challenge's profile, make sure you're logged in, and look at the time that displays in brackets next to the challenge time.
For me that reads,
Fri 16 Mar 2018 11:55PM UTC (12:55PM NZDT)
(and I mentally correct to 12:55PM *Saturday*, because NZDT is ahead of UTC.)
no subject
timeanddate.com is especially handy for converting - try here?
https://www.timeanddate.com/worldclock/converter.html?iso=20180316T235500&p1=1440&p2=tz_et
However, the simplest method may be to go to the AO3's challenge's profile, make sure you're logged in, and look at the time that displays in brackets next to the challenge time.
For me that reads,
Fri 16 Mar 2018 11:55PM UTC (12:55PM NZDT)
(and I mentally correct to 12:55PM *Saturday*, because NZDT is ahead of UTC.)