I haven't looks at the specifics of this flight or schedule but general comments...

There is no 40-hr rest requirement but there is a 30-hour requirement. 30-hours free from duty within the past 168 hours measured at the start of a flight duty period.

The other consideration for a long haul flight like this is the duty day limitation which is based on the number of legs and the report time in the acclimatized theater. They may be delaying the start of the flight duty period until it is within the window which allows a longer flight duty period which is needed for the long haul flight.

With the (relatively) new 14 CFR 117 flight and duty limitation rules, at least for pilots, we all pretty much fly to the regulation. There are very few additional restrictions added by the union contracts as 14 CFR 117 is, in most cases, more restrictive.

Another thought, though it wouldn't apply to this flight, is that once the crew rest delay is covered, they might not be able to depart on a long-haul flight due to noise curfews or based on the time that immigrations opens at the destination airport. i.e. can't arrive at 3am if immigration opens at 6am.