I doubt they do anything about TZ in Spanner since GPS time is not UTC (no leap seconds). In fact, UTC isn't even mentioned once in the paper. What is mention

I doubt they do anything about TZ in Spanner since GPS time is not UTC (no leap seconds). In fact, UTC isn't even mentioned once in the paper. What is mentioned however is the TrueTime API that models `Clock.now()` as intervals rather than a fixed timestamp.