I believe a courtship is as long as it needs to be. It seems like a lot of people rush into marriage thinking they have to follow a timeline. Yet, once they're married, they find out they still have a lot of issues they should've worked out with their spouse before entering marriage.
I am in a courtship and many married couples have emphasized, if not over emphasized, that the one thing a God-focused courting couple has on their side is time. Many married couples have told my boyfriend and I to take our time and realize that any problems/issues we may have as individuals and a couple are compounded once we enter marriage. So, understanding that, I don't think courtships should have a timeline especially if you're truly trying to prepare yourself to be married to this other person.
Of course, being in a God-focused courtship requires tremendous work regarding purity boundaries. Two years can be a long time to fall in love with someone and have to wait to share yourself. However, it can be done. I know plenty of examples including my own brother who dated my sister-in-law for seven years before marrying her. He's an extreme case, but it's encouraging, nonetheless. My boyfriend and I have decided to save our first kiss (to each other) for marriage, and we have no idea when we'll be able to get married even though that's what we're striving for.