settle this for me: how long do seo changes take?

Depends what changed. A title tag edit can show in results within days once the page is recrawled. A new page on a newish site takes weeks to get indexed and months to settle. Real ranking movement from content and links, three to six months is the honest answer, longer in competitive niches. The mistake is changing it again after two weeks because nothing happened yet. You never find out what worked.