None of the explanations below are correct. It is warmer but most people don’t have electric heat (resistive or heat pump). Fewer people are home but they are at work and commercial and industrial uses are the largest use. Electricity use peaks midday.

The drop is being caused by solar generation which peaks exactly during those hours. Behind-the-meter solar (and net-metered solar) won’t show up in the aggregate wholesale NYISO generation mix but it will clip demand in exactly the way you see here.

The morning and evening dips are generally caused by people operating ovens, microwaves, start-up of some factory equipment, but in this season, no A/C. A/C completely changes the curve as you approach June. Late afternoons become a single peak for the 24 hour periods.

https://www.eia.gov/todayinenergy/detail.php?id=43295

Warmest part of the day?