I found a pretty good line down last time I did this (2019), by luck rather than anything else. I aimed for the westerly point of the llyn and ended up in a shallow, mostly grassy gully. This brought me down to the remains of a stone structure which I assume is a sheepfold. The walls are shown on the OS map but it isn't noted as anything (looks a bit like a tadpole shape!). From memory there was a trod to Pen y Pass from here.
I've checked my split and it was 20mins which seems reasonable compared to others on the day and considering descending isn't my strong point.