The next stage was the "Brevet D" or Silver C which had to be done in two or three flights for Height Gained (1000m or more), Distance (50 Km +) and Duration (5 hours plus) Fewer than 300 UK Silver Cs had been issued at that time.
There were further stages possible, for Gold or Diamond C but I never got near enough to know what they were ! But only for distance and Height gained, even before FTLs came in.
(Duration for me was always less than 2 or 3 hours on single or twin engined aeroplanes. Or more like 15 hours on fours.)
Winch launches were the norm, and economic on petrol at perhaps half a pint per launch which might provide one with several hours of flight - if you found more lift, which might be a thermal, hill lift or if very lucky/ skilled, a Standing wave or a Cb.
Enjoy your Gliding
LT