If you book the two seperately...as in on your own..., you can do what ever you want. For example, you can book a four day cruise, then arrange for a 3,4,5...etc. day stay at a WDW resort. This usually requires you to make all of your arrangements on your own (transfers, hotel, park tickets, etc.) Some people like to do this because they can usually get better price deals on the individual parts of the vacation. If you book the actual Land/Sea vacation then you do have to do the Land portion first. Most people book this way because they enjoy the convenience of the "seamless" transition from land to ship and the ease of having everything booked at one time (but it will generally cost you a little more). Personally, I like the convenience of having everything done in one booking.