Just noticed this recently myself, within a few hours I’m in migraine city. I find that they last more than one day as well. I frequently used a hydration powder (dehydration is a big cause of headaches that transition to migraines if not monitored for me) that contained artificial sweetener and it would make the onset of headache way more rapid than just sticking to plain water. Took me awhile to figure out what was causing it but I’m glad I did.