Cocoa uses UTC internally. for all of its date/time calculations.
If you create an NSDate for now:
NSDate()
You get a date that is the number of elapsed seconds since midnight, 1970 in UTC time.
Dates only have time zones when you display them.
By default logging a date to the console logs it in UTC, which can be confusing.
If I'm working on a project that does a lot of date/time calculations I'll create a debugging method that converts an NSDate to a date/time string in the current locale, which is easier to read/debug without having to mentally convert from UTC back to local time.
I have never used Tempo, so I don't know if it is using date strings, NSDate, or "internet dates" (which are also in UTC, but use a different "zero date" or "epoch date")