An API returns a timestamp as UNIX timestamp at UTC and I would like to know if this timestamp was more than `x` seconds ago. As expected, this works fine with `os.time() - x > timestamp` in UTC, but blows up in other timezones.

Unfortunately I can't find a good way solve this in lua.

`os.date` helpfully has the `!` prefix (e.g. `os.date("!%H:%M:%S")`) to return time at UTC, but it seems that despite the documentation stating it supports all `strftime` options, this does not support the `%s` option. I have heard people mention that this is caused by Lua compile time options for a similar issue, but changing these is not possible as the interpreter is provided by the user.