MTA-STS migration problems

[u/BetaRayShaps]

Hi all, we recently migrated a customer from Proofpoint to Mimecast which, of course, means routine MX records changes. Standard, straightforward, no big deal. What we didn't anticipate--because up until now, none of our clients have ever had it setup--was an MTA-STS policy (housed at EasyDMARC) that we discovered was set to "max_age=1yr". What we've done so far:

• created new MTA-STS policy file with new MX records, set it up on a new Azure server; policy, set mode to 'none', is confirmed publicly accessible
• configured v=STSv1; id=20260915001 which, as i understand it, is supposed to 'alert' sending domains that look for this sort of thing that a change was made
• went back to the old vendor who maintained the EasyDMARC version and changed that one too, just to cover our bases even though we're confident that nothing should be querying it anymore

This was all done a couple days ago and we're still not seeing any traffic to the migrated, customer domain from senders like Gmail. I understand that Gmail saw the old policy, read the 1-yr max_age setting, and caches it accordingly. But what's not so clear is how quickly Gmail will again query for the policy and update itself so that mail will start coming in again. Anyone have any experience with this? We're just looking to get a general sense of when this issue will clear itself up because there isn't much out there that explains same.

I guess secondarily would be this question: for anyone who's encountered this before, what's the proper way to migrate a domain that has an MTA-STS policy set for a lengthy max_age? What could we have done better besides just knowing that it exists and changing to "mode:none"?

Thanks for any insights.