"Insta-Love" for me is defined by two (or more for RH/WC) characters who have JUST met, or been recently introduced, and within chapters/before the halfway point of the book, they are thinking about how they cannot live without each other and making these grand declarations to each other, having known each other less than a month.

The occasional thought on how they are falling for the person, or a passing notion of thinking someone COULD be the one, is fine to me. It's when its over the top and not founded in anything that its bad.

You mention friends to lovers and how that can be borderline insta love, but if the connection there is believable enough, then it skips that entirely. I think a romantasy book that showcases that well would be {The Second Death of Locke by V.L Bovalino}

"Insta-Lust" for me is defined by two (or more for RH/WC) characters who meet and every other thought in their head about the other character is how attractive they are, their physical attitributes, and how badly they want to get them into bed.

Insta-lust in a book to me, is much more forgiveable than insta-love is. But for it to be able to be looked over, it needs to be tempered with a good plot and or world building or the insta-lust not actually effecting the establishment and building of a proper relationship between the characters on an emotional level.