This not an easy question to answer because it is possible for people to meet only a few times and 'live happily ever after' By this, I'm being facetious. I mean, having a reasonable loving and life long relationship. This happened to War Brides in World War Two. Some were successful in the long term. I expect the majority were not. One would have to get hold of the statistics.
Then there are the cases of couples going out together - or even living together - for years. But once it came to their getting married and the days 'of beer and skittles' were over and that dreaded sense of responsibility and having to actually make a life together, is too much and they separate.
This business about the 'right one' is a bit of a misnomer, too. I'm of the opinion that any reasonable well adjusted and mature male could marry just about any woman in the world if she, too, was reasonably well adjusted and mature. I'd say compatibility rates far wider than is often believed when it comes to finding a partner for life.
But how few of us don't have our hang-ups and idiosyncrasies and are really world-wise and loving human beings. It's no good marrying simply because 'you're lonely.' You could well be just as lonely in marriage.
To me, I would say compatibility, friendship, mutual interests and the willingness to be a friend, lover husband or wife and to let the other be AS THEY ARE not how you might later like them to be when the initial novellty of being together wears off, is probably what is most important. 'Being in love' is a need. Loving is something else again. And sometimes this only develops over time.
How long we're willing to 'hang in there' and stick by those marriage vows is what is important. How long before you make that commitment depends entirely upon the individuals concerned.