Different timeshares do it different ways. The rule of thumb is that there is no consistent rule of thumb.
We formerly owned an Orlando FL biennial timeshare that billed us every year. At the same time, we owned a Kissimmee FL triennial timeshare that billed us for the full use-year maintenance fee during our use year, then nothing during our 2 off years.
Later, we got rid of both of those & got a triennial points unit in Las Vegas that every year bills us for 1/3 of the use-year amount.
I hear that some timeshare companies (e.g., Wyndham) bill monthly for maintenance fees. Some might even bill quarterly.
So it goes.
-- Alan Cole, McLean (Fairfax County), Virginia, USA.