It's not just time zones and leap seconds. SI seconds on Earth are slower because of relativity, so there are time standards for space stuff (TCB, TGC) that use faster SI seconds than UTC/Unix time. T2 - T1 = [God doesn't know and the Devil isn't telling.]
That one's really good.
Which one is it?
And is it 2011/2005 or rather 1911/1905, 1811/1805,...?