Hence the scare quotes around simple. The math is in no way straightforward, but it's nonetheless math, esp. once you have the TZ information (if required) in front of you. The point was that there are plenty of operations within a typical server-side codebase that either involve little-to-no syscalls (tagging a record with the current UTC time, or converting a UTC timestamp to an ISO formatted date and time for serialization on the wire, e.g., JSON) or are forced to hit really expensive syscalls, rendering a quite-likely-cached-in-RAM stat() moot (logging, SQL queries).