aidle:
There are many factors which would need to go into a study on the relationship between dating length and divorce.
To do an accurate study, you would need two groups who were the same in hashkafa, social pressures, upbringing, and all sorts of other things. (This is impossible.)
A comparison to chassidim is therefore disingenuous since their hashakafa and society is different.
Likewise a story about a couple who dated for 6 months, since they were either relatively modern, or had some serious issues to work through. (If the latter, we can speculate on why they got divorced)