March and April warmth slopes did not differ clearly for spring greening duration in four eastern US camera samples in 2008-2023

We tested whether April warmth had a more negative link than March warmth to the time from 10% to 50% spring canopy greening. Six of 55 available camera sites passed fixed coverage and date-quality rules. Four tests used two latitude bands and two time periods in 2008-2023. Models controlled site means and site-specific time trends. April-minus-March slopes were +0.01, +0.84, -2.09 and +0.39 days per C. All four corrected intervals included zero under both year and site clusters. Source date intervals also permitted both signs of each fitted contrast under an independent endpoint-error bound. Three-day processing changed one contrast sign. The data do not establish a common contrast or its absence. Few sites, few years, uncertain dates, shared weather and fixed calendar windows limit inference. This test concerns canopy timing, not species counts or pollution effects. The package includes code, aggregate estimates, a figure, source hashes and external retrieval instructions.