Data points:
Tue 08/03/21 - downgraded CSR to regular CF (already have CFU)
Thu 08/05/21 - received the electronic document on Chase.com indicating new terms
Fri 08/06/21 - applied for CSP online, did not get approved immediately. I've learnt that prepaid cell phone numbers seem to get flagged by security checks (e.g. including IRS), so I called recon a few minutes later. They asked a bunch of verification questions, then reallocated credit lines, for an immediate approval.
Interestingly, even though I applied before 8/15, it does appear that I qualify for the $50 hotel credit, as it shows up on the UR portal.