At about 18–20°C, about 6–8 hours of continuous leaf wetness can trigger downy mildew on cucurbits, while powdery mildew can germinate without free water — so which timing carries more risk for downy mildew? I’m asking because moving a pivot from 10 pm to 5 am last July cut lesion incidence by roughly half in one trial block.
In my cucurbit blocks, starting the pivot about 60–90 minutes before first light and doing a faster pass so foliage is dry by about 9 a.m. cut downy mildew the same way your ‘5 am’ switch did, by keeping wetness under the 6–8 hour window. Small caveat: if it’s foggy and RH stays >90% after sunrise, the benefit disappears — @OP, have you tried tying start time to a cheap leaf-wetness sensor?
Pre-dawn is usually lower risk for downy mildew because you’re not stacking extra night hours of wetness — “dew + dark = trouble” — and if your pivot’s still over-canopy, switch to drop nozzles and run a quicker pass so leaves dry right after sunrise. Watch the dew-point spread (T−Td < about 1°C means they’re already wet) and time runs with NEWA: https://newa.cornell.edu; in hot, windy nights that advantage narrows.