A neighbor owns a vacation timeshare condo in TX. They have spent about 5 months off and on at this place this year. The rules say they get one week per year. When I asked about that she says they have bonus time but won’t go into details. Is it really possible to get that much time? How does that work? Thanks!

You get as many weeks as you buy. You buy a timeshare by the week. You can also rent other peoples weeks if they are available.
It depends on how much you spend, and how many other people you share it with, and what their schedules are. If it’s open, they can use it.
I’ve heard that you get a few extra weeks but never heard of almost a year and a half that just don’t happends to regular tendants. Maybe they have some special arrengement that don’t want to tell.