Haha, good question! Sounds like we need a committee.
I'd say they are "green" as soon as it's your fixed address.
I'd say if a location becomes your fixed address, then any sighting obtained using non-motorised transports from this location might arguably be seen as "green" -- including any sighting that would date from before this address was 'officially' fixed.
Any rule will be arbitrary, anyway.
(A non-motorised list is in principle associated to a fixed "base" (the location where you start and end your birding trips). The very principle of combining lists associated to different bases (as we do here) will always be a bit questionable. For instance, I see no good reasons why a single observer would not be allowed to keep several simultaneous non-motorised lists, associated to different bases. You might, for example, wish to keep a list associated to your everyday address in Germany, and a second one associated to your family's place in the Netherlands, if you bird from there as well using a bicycle. Why not call two such lists "green", when considering them independently ? Not doing so would mean losing an incentive to bird "green" when you are in the Netherlands, which would arguably not be a good thing. Combining these two lists into a "global green list" would however quite clearly be objectionable. But, then, combining your Dutch and your German lists into a single "global national list" would not make much sense either...)
I added a Melodious Warbler today which has been singing on a slag heap just over an hour's cycling to the south.
I moved to an area ~100km S of Brussels for a few days (last Wednesday to yesterday), and actually got MW -- a fairly normal bird down there -- two days earlier.
Also a Black Stork, which was new for the common list.
(Meanwhile, a singing Thrush Nightingale and a King Eider have been found on the Belgian coast... Should be able to try these tomorrow, if things go well.)
