Just to be clear, the 1.5 months is very much a "best case" estimate. It could easily be a month or more later, if we found any significant issue during testnet testing.

It wouldn't even have to be some new issue, as we're also doing more testing of the longstanding functionality of the blockchain that has never been fully tested to my complete satisfaction.

A minor example of such a longstanding problem was the cpu loading I mentioned in the post that we found when our testing node wasn't connected to any peers. But that's a relatively minor issue that could be fixed later without a hardfork (and it is also a small enough issue that we can just fix it quickly). If we find any definitive consensus bugs that need fixing during our testing, they could easily delay the hardfork by several weeks.