I would think that their servers were using NTP so the time should very accurate.
You can use the Time library to do the conversion.
https://www.pjrc.com/teensy/td_libs_Time.html
But it doesn't support time zones.
Timezone shifting is easy as you simply add/subtract the appropriate number to seconds to shift the timestamp to the local timezone.
However, it gets complicated to know how to handle daylight savings time (summer time in EU).
To do that you can add the Timezone library:
--- bill