IMO, neither comes that quick, although we certainly can have fairly quick attractions to and strong dislikes for people. Thing is many people are very lazy about their words---both 'love' and 'hate' are thrown around way to easy and quickly. i say again, more than once i've butted heads with someone on first encounter, but we both made an effort to talk thru it and settled into a mutual respect and sometimes friendship. i don't even use 'hate' about my exes and #3. (i tend to hate certain behaviors but still be able to see the good or neutral qualities the same person is capable of as well.)
And it isn't just about 'time', it's about the effort the two put into relationship building. Some relationships that begin based on immediate attraction do well, even if they don't last 'till death do them part', because the people involved still put effort into the relationship. We're seeing more younger couples all the time who manage to 'co-parent' successfully post going their separate ways. Trust takes time and a variety of life experiences to build, and it's the hardest thing to get back once broken/betrayed. That's the problem with 'instant' love you don't know enough about each other yet. If you 'hate' quickly at worst you might be depriving yourself of getting to know someone you could benefit from knowing. But if you love and trust too quickly--the worst case scenario could be serious emotional damage to you, your children even the other person.
We have to remember that marrying for romantic 'love' is a fairly recent development in human relationships. My Hungarian Grandmother was pushed into a marriage with a 20 something when she was just 14. Luckily for her he had approached her family because he was head over heels for her. She ruled their roost, and he stayed in love with her despite not being blind to her flaws judging from things he told one my Aunties. In some countries arranged marriages are still fairly common. From what i've read, some of them 'come to an understanding' and keep up appearances, some actually come to love each other deeply over time.
