I don’t know about King’s Cross (except the chap in this Holborn Office who commutes in from there gets in screamingly early <08:00 and similarly knocks off at 16:00).
But at this end – as you mentioned Snow Hill – just a bit further away nearby is Stonecutter Street where hundreds of bikes are stacked during the day. The Sercoids are there to make space in the morning and you can pretty much always get a bike up to 18:30 and are very friendly.
Of course BBs are used for commuting – if you’re lucky – why else were the huge Waterloo dock + bike store built. But the aim seems to be to do little or no redistribution, which must be costly (manpower). For instance for the third morning in a row, having made the unpardonable error of getting into Waterloo after 08:00 I ended up walking into Holborn – that’s a zig-zag route passing 13 (yes 13) docking stations containing nothing but red-lighted bikes until it is not worth trying to find one and walking the rest of the way.