Can we add informational popups/alerts to users on the forgot password page or login screen?

Can we add informational popups/alerts to users on the forgot password page or login screen?

I'd like to tell my users that it may take up to 30 minutes for their password is replicated to the helpdesk? our AD Sync tool runs every 5 minutes i believe, so its just when users are trying to get back into the helpdesk before the delta sync runs to pickup new password changes. 


found this page above, so i understand we can play around with the HTML, and im all down for that if i just knew what we were allowed to add...no javascript i bet right? just css and html? Im also assuming the div tags that actually load the login form isnt customizable...for good reason im sure, but it would be nice to spit out a simple page alert that warns the user that it could take up to 30 minutes before they can use the new password on the helpdesk. 

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