Two passes because the offset we need is the one in force at the answer,
not at the guess: on a DST changeover day the first pass can land an hour out,
and the second pass corrects it. A wall time that a spring-forward skipped has
no exact answer; this settles on the instant one offset-step later, which is
the same choice Date makes.
Wall-clock components in
zone→ UTC seconds.Two passes because the offset we need is the one in force at the answer, not at the guess: on a DST changeover day the first pass can land an hour out, and the second pass corrects it. A wall time that a spring-forward skipped has no exact answer; this settles on the instant one offset-step later, which is the same choice
Datemakes.