it was 0.505s late.
Sounds like racing. You cannot be a winner if you come 0.5 s later... 
Yes, this time it was correct...but we have lost a couple where we were clearly first.
The 0.5s means that we had already started working on a new network block, 421430, but a share/block then came in for the previous network block, 421429, so was guaranteed to automatically be flagged as an 'orphan' less than a minute later by ckdb since it didn't match what the pool's btcd had already decided 421429 was (0.5 seconds earlier)
The only way around this would be to try to force an orphan race and hope we got a double confirm.
But purposefully creating an orphan race after a block change is frowned upon and we don't do that ... though I've no idea if other pools do, or not.