I don't have any inside knowledge.
As you point out, it leaves 30-45 mins late and arrives 45-60 mins late for months.
The great circle mapper says it is following the shortest route.
Its flight time is consistently ~30 minutes longer than the planning software says it should be for an A380.
It ~never arrives before 5 pm going back 6 months despite a 4.35 arrival time.
Maybe the actual arrival slot is after 5pm? But pure speculation.
Interesting.