Information that I have indicates that they are all generally open until 10pm during peak seasons, including SAB. However, the resort brochures (those papers they hand-out at check-in) indicate that pool hours are subject to seasonal fluctuations. If you've heard of SAB closing at 8pm, it may be during one of the slower (cooler) seasons. If so, the other resorts were likely on similar schedules.
Management will also alter schedules on the fly in response to weather patterns. If you're visiting during the winter months and the forecast calls for a high in the 50s, I doubt you will see lifeguards standing on duty until 10pm regardless of what the schedule might have been.
In other words, it's a pretty fluid thing.