He was in bed by 8:00 p.m.
No, they are much more likely to be resetting his circadian rhythm. With his dementia, he very likely has sundowners, which is a classic symptom of dementia. Sundowners occurs when they get anxious and upset with the diminishing light levels as the sun goes down. Any nurse that has worked with dementia patients can tell you this.
He might be sitting in the basement right now, but willing to bet that there are massive lights on, that will mimic the stage setting for the debate. The light level will help with the sundowners and emotionally prepare him for the environment.
Perhaps Trump should suggest a calmer, quieter environment with lower lighting for the next debate.