I think that the couple should date as long as it takes to be comfortable and sure of yourself.
Personally i dated 4 weeks (7 dates and one very short one where we went out to get engaged).
i have a friend that dated 7 dates in 3 weeks.
i have another friend that dated 6/7 times in 1 week. (ok that is a little crazy- but what can an out of towner do?)
then i have friends that dated for a few months.
anything goes as long as you are not continuing to have a good time, but rather to find your spouse.