It's 11.2mm diameter, two 0.22 cal bullets side by side.
In our league we don't shoot to a time limit. Each card has ten roundels and you place one shot in each roundel. Two such cards constitutes a course of fire, thus 20 shots, and both cards must be shot on the same day, but not necessarily - and not practically - in successive details.
At a typical club meet, we get about ten or so details done in just over two hours, so each detail lasts about 12 minutes including changeover time. Actual shooting time per detail is less than ten minutes normally, and a bench rest card of ten shots takes a little bit longer to do than two 5-shot standing cards.
It's normal to shoot one card, then miss one or two details and shoot the other card after a break.