If you use the quick edit the time will contain a {2}. After refreshing, the time will shown correctly so it seems to be a js issue, but I'm not sure whether it is necessary to fix it now or whether it is better to wait until we have jQuery.
Hi,
Thank you for your report. We have pushed this issue to our Github repository for further analysis where you can track our commits and progress with fixing this bug. Discussions regarding this bug may also take place there too.
Follow this link to visit the issue on Github:
https://github.com/mybb/mybb/issues/18
Thanks for contributing to MyBB!
Regards,
The MyBB Group