Is the basic deal that you do it as a 400 up the Western leg ( control @YH, continue to Menai Bridge, and loop back to YH again ) grab a bit of kip and then a 200 home down the Eastern leg?
As everyone else is ignoring you Feanor, yes, except that it’s not quite 400 before the YH, and more than 200 afterwards. Also, it’s 619km rather than 600km, and, as with all over-distance events, the extra comes at the end when you’re tired rather than the beginning when you’re fresh.
In the past I’ve tended to get back to Kings YH at about 2:30-3:30 and left at 6:30-7:00. There will be more than 50% of the field who have arrived before me, but there are always some people coming in as I’m leaving, and they usually manage to finish in time.
The ride on the A470 (I think) to get from Maentwrog to the YH is usually the most gruelling cycling I experience every year, purely because of tiredness (and a tedious climb to Trawsfynnydd). Conversely, day 2 of the BCM is always a highlight of the cycling year, because I’ve always felt so good – at least as far as the 600km mark.
One of the highlights is the final control at Weobley. By then you’re back in England, so the roads are rougher but the weather is better. The control is a receipt from the village shop, but there’s a village green opposite and you’ll find quite a few relaxed BCMers, relaxing and chatting in the afternoon sun, some lazing in the blossom-strewn greensward, supping their Frijjs and munching on their Ginsters, job nearly done. It may not be quite so relaxed for those behind, or for those ahead who raced and are home while I’m still doing my greensward-lazing.