This is what points managers do with the popular Worldmark and Wyndham resorts. You can book 365 days a year straight out if you so wish and you have the points to do so. For example, Marina Dunes is one of the popular resorts (near Monterrey), you can book starting in April through October in one booking and rent those weeks out separately.
WM has put in some new rules to limit the ability to rent out weeks separately from a long booking. However, if it is for your own use, you can book as many nights as you want. The online calendar will only allow up to 30 days but for more than that, you simply call in. Once you book over 30 nights, the Transient Occupancy Tax charged by many localities no longer applies.
Most think timeshares are week based. This is no longer true. You can buy points and book any number of days you want, depending on the rules for that system. With WM, you can start any day of the week for any length;3 nights or 13 or 23 or 33 etc. You have to book at least 7 days in red season from 13 months to 10 months before the start date and, at 10 months, you can book less than 7 days.
Each system is different and it makes no sense to try to figure out the rules of each before narrowing things down. Start with this thread
http://tugbbs.com/forums/showthread.php?t=208742 and that should help narrow down the options to a manageable few. The real key is location and quality.
Tuggers Ron and Joan are timesharing full time using a combination of timeshares. Their blog is here:
http://ronandjoanjourney.blogspot.com/
So answer the questions in Denise's thread and narrow down which systems best fit what you want. Then start investigating those systems. It might be that a series of weeks works for you or a couple of point systems makes sense. Bottom line, the 3 months isn't a big deal in timesharing. 'Regular' (if there is such a thing) timeshares can work well for you especially if you want to go to different locations.
Sue