My Guild group tried to do a boss hunt last night. I posted my character at the spot where the Walker is normally located, though it wasn't there in the afternoon. (Our op was to set up summons in the PvE instance.)
Later when I logged in to summon the group. Once again, It wasn't there. (It is there in the PVP instance but not PVE)
Now, the next day, I log in and it's noon and the walker is still not there in PvE.though it IS up in PvP.