Lughnasadh
Long story short, it’s not the midpoint between the equinox and solstice. That’s August 7th this year, which means my Harvestpoint runs from sunset on August 6th to sunset on August 8th.
My High Holidays begin at sunset the day before the Cross Quarter Day and last until sunset the day after.
My Solar Festivals begin at sunrise the day before the equinox or solstice and last until sunrise the day after.
Harvestpoint differs from Lughnasadh, but that is a good place to begin your studies.
Let me suggest Lammas from Mike Nichols The Witches Sabbats as a resource.