Al, your sunrise time looks pretty accurate. An online almanac gives sunrise in Brussels in June to be 5:35AM, and in Paris as 5:51 AM. So, as Cambrai is between the two 5:41 would be in the ballpark. Basically he landed just after sunrise.
Bishop also reported very low cloud, mist and rain when he took off and crossed the lines, which didn't help his navigation. He stated that he circled and found an aerodrome that was vacant, in frustration he wandered about until coming upon another. It is no wonder that he didn't recognise it, I doubt that any of us (who are pilots) would do better considering the poor quality compasses of the day and the conditions (darkness to half-light at best; low cloud, ground mist and rain).
In his biography (Horses Don't Fly)
Frederick Libby thought that Bishop was full of it (he didn't give a name, but it was apparent who he was writing about). In particular, he mentioned that if Bishop had been at the aerodrome that they thought (Estourmel) then he was certainly lying for Libby had photographed it many times and there wasn't a tree in the area. Can anybody check this with WWI air photos of Cambrai and it's brace of aerodromes?
Miles