Quintas across the Cima Corgo report veraison arriving ten to fourteen days ahead of the ten-year average, which puts the first Touriga Nacional pickings in late August rather than mid-September.
The practical consequence for visitors is simple: if you travel in September you are more likely to see fermentation than picking, and the lagares will be busy at night. Ask before you arrive — most quintas will let a small group watch the treading if they know you are coming.