This wasn't my experience at all. I had 3 flights, and tried to use live chat to select bulkhead seats at 96 hours before each flight. In each case I was told none of the bulkhead seats were available. In one case I was told no seats were available at all for selection, although there were empty seats on the flight - including bulkheads.

However, when I checked in at 48 hours before my first flight, I was able to see bulkhead seat availability (and select them) on my subsequent flights, even though these flights were obviously more than 48 hours later than when I checked in. Many bulkhead seats were showing as available on those flights, but not the first flight (which did have other regular seats available to choose).