I known that it's better if I can pinpoint exactly calendar time, but even Theymos have not cared about that
It would have been much more considerate if theymos would have sent the first Merit at midnight exactly

To take away all doubt:
the first Merit was this one:
1516831941 1 2818066.msg28853325 35 877396
Use
EpochConverter to convert 1516831941 (Unix Time) to GMT: Wednesday 24 January 2018 22:12:21.