If you are coming off a staff job and non-current/non-recent, you can expect to realistically spend 12-18 months at the regionals.

Might it be less? Yep. More? Certainly, yes.

I know of non-current mil guys called up for major interviews right after updating their apps with their fresh, new type rating and were at the regionals only barely long enough to complete IOE. I also know guys who spent 2 years at the regionals waiting for the call and upgraded to Captain. All of them were guys with good resumes and no major skeletons in their closets.

Be emotionally and financially prepared for 2 years, and be happy when it doesn't actually take that long.