Autumn date intervals were wider on average in four selected eastern US camera samples in 2008-2023

We compared spring and autumn date precision in 103 paired camera-years at eight eastern US PhenoCam sites. Each region had four fixed sites in 2008-2015 and 2016-2023. At 50 percent greenness amplitude, the equal-site geometric autumn-to-spring interval width ratios were 1.37 and 1.25 in the North, and 1.60 and 2.43 in the South. Only the early North interval stayed above one after four-test adjustment with a crossed site and year bootstrap. All four ratios stayed above one when any one site was removed. Dividing width by seasonal transition duration gave ratios of 0.95-1.65; all four adjusted intervals included one. This check did not establish slow seasonal change as the cause. Four sites per region, selected complete pairs and shared source processing limit inference. The study audits timing precision for climate-response studies. It does not measure a weather effect, pollution effect, species loss or a causal climate trend. Code, source hashes, aggregate results and a figure support reproduction. External source records stay outside the bundle.