September, October, November, December is 4 months. This past year it stayed up until the end of January (no that is not normal and was likely so they would have a crowd-eating ride while they waited for MMRR to open), so it was 5 months of NBC and between the changeovers, 6 months without the regular Haunted Mansion. That is way too much for ANY overlay.
It also doesn't make a whole lot of sense this particular year to have it switch so early. The new HM movie comes out on July 28th and people will get to ride for a whole 2 weeks before it shuts down. Seems like a missed opportunity to push the schedule a bit, IMO.
Like I said earlier, give NBC a year-round attraction. It’s popular enough for it and won’t take away from the also immensely popular HM.