Time is not nearly as important as being with the "right one". Anyone who is married will tell you that nothing "magical" happens after you say, "I do". You're still the same people.
It's nothing wrong with waiting to put yourself in the best possible financial position to build a future together. Too many couples go deep into debt to have a lavish wedding and they begin their marriage under a huge financial strain. Keep in mind the wedding is (one) day and marriage is supposed to be for life.
Most people generally take up to a year to plan a wedding and therefore my guess is the typical engagement lasts anywhere between 12-18 months. Ideally a man should not propose unless he has a timeframe in mind otherwise many women will feel as though the only reason he gave them a ring was to "shut them up".
If you're not looking to have a "fairytale wedding" then you can always just go down to the courthouse tomorrow, or fly to Las Vegas, or bundle the ceremony with a "destination wedding" such as those often done in Cancun or Jamaica at an all inclusive resort. A few employees will serve as witnesses or maybe you have a couple of friends who take the trip with you. Another option is to tie the knot on a cruise ship. These options allow you to combine your honeymoon and wedding ceremony at a price which is often much cheaper than having a wedding with lots of guests and going away for a honeymoon. Some people have been known to get married while away and have their reception planned for when they return. This way they can still get gifts and party with friends.