This is how you open the Dreamer's Bounty. I know in the video i kept calling it the dreamer's stash, but I meant bounty lol. I also already opened the chest on this toon which is why you don't see me click it in the video. You have to get a nearby preying dustmoth to attack you and get its drowsy dust debuff put on you, and kill it while the debuff is still active, then open the chest with the remaining time you have the debuff (you have to be quick).
Hope this helps!