I'd like for the dungeons to also be explorable in the overworld map

[Sylve]

I don't want them to be open world dungeons I just want the locations to be explorable in the world.

This would be an issue in that they would need to physically locate every dungeon in the world. Essentially expanding the map.
Most MMOs that i'm aware of only have faux entrances to dungeons with a threshold that loads you into the instance when you cross it. There won't actually be an explorable zone behind that entrance. Usually just a wall or corridor that's angled in a way to appear that theres something accessible on the other side.
The actual dungeon you travel through is its own zone that doesn't exist on the world map, which is why if you fall through the floor and look up, all you see is the dungeon floating in a skybox.

So by asking for them to be explorable in the open world, you are actually asking them to physically place the entirety of the dungeon map into the world zone and have it be sized appropriately. Theres also the problem of Hard Modes having different layouts. Which one do you put in the open world?

Its too much work for too little payoff. Most would visit once to sightsee and then never go back. Sure you'd get the odd few that spend a lot of time in them but there just wouldn't be enough to justify the workload.

I'd be fine just being able to walk around and explore a cleared dungeon without a timer. Or at least with a longer one. There are some great locations that would make for incredible screenshots, and there isn't time to do that while fighting.

Average clear time is 20~ minutes.
You have a 90 minute timer to start.
After clearing, just hit Return to go back to the entrance and then you have over an hour to make your screenshots.