Im not buying the 30 minute initial delay equals 1 hour overall as flight time would still be same length.
The PP has his own rules for math.
However, I have actually had it happen. The New York Airports increased their "cushion" time. My flight times were changed. I left 5 minutes later and arrived about 25 minutes later. It was simply due to an increase in the ATC "cushion".
On the other hand, last week (again involving NYC), I took a VDB for a flight 90 minutes later. Since the later flight ended up leaving NYC at the perfect window, whilst the earlier flight had a slight ground delay at take off and the later flight had a bigger/faster plane, our arrival time was only 60 minutes later (and I got $400 USD for my troubles).