I'm wondering if every nightmare dungeon can be the whisper quest of the hour. It seems most of the hourly ones are non-Nightmare, but always have one vault that rotates between all 4 vaults, so I keep one of each of those. I just want to be able to do the one vault and the one nightmare dungeon to get 10 whispers each hour, but I never seem to hold onto the right sigils.

I think you mean that every sigil that drops during the hour is a whisper nightmare dungeon? If so, I agree.

Now that I think about it, my real question is which NM dungeons can be selected to give the 5 whisper rewards.

look on da world wide web it is very helpful

I actually have looked quite a bit, so decided to post here. Doesn’t really seem to be anything being tracked or updated so I’m just working on a list of my own. There are tons of NM list and even basic dungeon lists, but nothing simply showing which NM dungeons can be selected for the whisper quest, which maybe means they all can be. It doesn’t seem to be a standard rotation as I’ve seen the same one pop multiple times in a day. The vault is for sure at least locked to one of the 4 and is always up though.
So far I think one of the four vaults is selected each hour or so. Then my theory is that one open world nm dungeon is selected. I’m collecting one of every sigil so I can basically get a whisper cache of the two dungeons.

sry i cant help