The dates for the particular three pricing seasons are generally the same every year except that the start and end date for each one might move a tad (a day back or forward).
May through Sep is the cheapest at $35 after 10. During that time the cost of a round for anyone staying on site and playing after 10 is usually $45 at the Palm and Lake Buena Vista, and $55 at the Magnoilia and $55 or $60 at Osprey (Eagle Pines is closed). Those seemingly low regular prices are due to the summer "price slice" which lowers the higher morning rates at 10.
The October to mid-Jan $50 cost compares to regular rates for on-site guests that are usually $85 for Palm and LBV and $110 to $120 for Mag and Osprey.
The $89 after 10 peak season rate compares to reular on-site guest rates of $135 for Palm and Mag to $155 to $165 for Mag and Osprey.
It is generally hot after 10 during the $35 season. About mid October through mid-April are more comfortable. You can get some cold days Dec through Feb. November after the PGA tournament is one of the better times to play Palm and Magnolia because of the extra effort they put into getting those courses ready for the PGA event, although the courses are generally fine all year.