hmm...I think spending quality time is the most important. You
can spend 4 to 5 years with one person, but if it is not quality
time, you still wun get to know him well. But you can spend just a
few months, but truly use the time to communicate and know each
other, then that will be quality time, and you will understand
him/her well enuff to know that he/she is the one for you 
just my opinion 
i.c.y