I disagree with many, I think it can be quite quick, and I don't think it has to be just lust.
I think it depends on the circumstances in which you meet, how much time you spend together and how quickly you get through stuff. Eg say If you swipe on a dating app, decide you are attracted and then meet once then date weekly, go on holiday after 6 months, meet their family after a year, it's different to say growing up with a friend and knowing them and their family and friends inside out, and then living with them and spending every waking hour together, and talking for 5 hours every night for a year.
Plus meeting someone at aged 15, 17, mid 20's, post divorce, may mean you are in a different place, seeking slightly different priorities.
The first time I met Dh was re a property. It wasn't a date, nothing romantic. I was shocked at my reaction re what a good basic sort, solid morals he was, the way he treated others generally. We spent so much time together we'd got through all the nitty gritty, all the basics, all the childhood memories, morals and views on fidelity etc very quickly, met all friends and family. It wasn't whirlwind it was slow and steady, but quickly, efficiently and detailed.
I knew immediately. What did I know? Not that he was 'the one', I never saw it quite like that, but I knew he was good, had all the qualities I valued. That hasn't changed after 25 years of marriage.