how long should you chat with a couple before actually meeting in person

we've had every variation now... met someone after 4 days of chatting and it was amazing, met someone after 6 weeks of chatting and it was a flop, met someone after 2 days and it was a disaster. so theres no obvious correlation between chat length and meet quality from our experience but i feel like there must be a sweet spot. what do you lot find works? is there a point where chatting too long actually kills it because youve built up expectations that cant be matched in person? im asking cos we've been chatting with a couple in wellington for nearly 2 months now and im starting to wonder if were just pen pals at this point