How may seconds for a shot of espresso?

Texas Coffee School has awesome courses such as 3-Day Barista + Business Workshop, 2-Day Barista Training Workshop, Beginner Barista Class, Coffee Brewing Methods Class and Coffee Cupping (tasting) Events.

Until the shot starts to blond (go lighter). Typically this about 25 seconds although this depends on the coffee beans used. If it is significantly longer or shorter it usually means something has gone wrong. Either the grind is too fine or too coarse, or it has been packed too tightly or loosely. Adjust these things until the time for a 25ml - 30ml shot takes about 25 seconds. Don't get too hung up on the timing though as the visual cues are much more important.