We have a Fairfield timeshare, so I may be able to help. THere are at least 3 different Fairfield ownership plans. If you have a fixed week plan, you must check in on the specified night and use the week as it was purchased. If you have one of the point system plans, you can check in on any night. There is not a minimum stay, but you must have enough housekeeping points to go along with your occupancy points. If you stay only a couple of days, you could run out of houskeeping points before the end of your year. In that case, you can pay a small housekeeping fee.
Fairfield can be a pain. Again, depending on your plan, there is a limit to the number of reservations you can make in a year (even if your travel is in different use years!!!). Exceed this and you pay $25 per ressie. I have been told that I couldn't reserve a larger unit even though I had the points to do it. On arrival at the resort, I again asked if the larger unit had become available. I was advised that they had some open but that "they have to be saved for VIP members in case one shows up at the last minute." OK, I have been trying for 9 months to get the unit I have the points for...and as I stand here at your desk on check in day you tell me that you need to save it just in case someone else drives up and wants it???? What is the chance that someone will show up????
There is no exchange fee if you stay within the Fairfield system.