Originally Posted by
jc94
It's 240h before your flight in the timezone flight leaves from
I also suspect it becomes 239 or 241 hours briefly when the clocks change.
In my experience, the one-hour error is not just when the clocks change. I've often had the experience of not being able to upgrade for AC 34 until 167 hours prior (in the case of a 7-day window) in periods when SYD has daylight saving time and Canada does not.