That's correct.

And again, you need to ensure that the length of your trip will not exceed the maximum stay permitted by the tariff. In other words, if you purchase one of those cheap fares floating around that permit a 30-day maximum stay, but you really intend to stay for up to six months, when you go to change your ticket, you'll need to buy-up to the higher (as well as pay the change fee) fare -- often this is more costly than doing it up front.