The PHL Amex lounge took about 10 months from initial announcement until opening (which felt like an eternity throughout 2017). The PHL AA Flagship lounge still isn't complete, despite being announced almost 7 years ago (granted Covid is partly to blame).

The best indication that the Amex Lounge construction was almost complete was job postings ~6 weeks prior to opening. I bet once job postings go live for the Chase Lounge, we'll see chatter on here about it. I wouldn't hold my breath until that point.