On a clear day in June the terrace has sun 09:10–19:40, about 10.5 hours in total. In short: sun at lunch, afternoon sun and evening sun until 19:40.
The story of Brasserie Elverket
Brasserie Elverket occupies a former electricity substation on Linnégatan 69. The building was designed by the power company's own architect, Gustaf de Frumerie, and opened in late 1925 to secure the supply to Östermalm. It was the last substation in Stockholm to stop delivering direct current, as late as 1973.
In 1997 the building was converted into Dramaten's Elverket stage, and the theatre restaurant Brasserie Elverket opened at the same time. The city museum has marked the building as particularly valuable.
Sources: Wikipedia: Östermalmsstationen · Brasserie Elverket
How Stoligt works it out
Every ten minutes we draw a line from each terrace toward the sun and check whether a building or hill is tall enough to block it. Building heights come from OpenStreetMap and ground heights from Lantmäteriet, the Swedish mapping agency. The times assume a clear day, so clouds are not included here. They are on the live map, which shows today's weather.
Trees, parasols and awnings are not in the model, and we don't know exactly where on the pavement the tables stand. Treat the times as an educated guess, often accurate to within ten minutes.