As one who loved Oblivion back in their childhood, I really admire the effort that went into this mission - though it also has to be said that levels in Oblivion were... not so great (especially on a Thief scale), so as soon as you put down your nostalgia glasses, it becomes clear that this is an average map (at best). I'm talking about the layout though, the portal effect this mission has was executed surprisingly well!
Some things that bothered me:
- While you're figuring out the puzzles, you need to run back and forth a lot! It becomes old quickly - and makes the otherwise interesting (though one of them makes not that much sense) puzzles a bit tedious.
- There is one jump that is so tight, it's basically impossible to make it at first try. It's basically mandatory to make a quicksave before it and keep trying till you can finally make the jump. Extremely annoying.
- SPOILER: When you finally get the hour glass, the mission does an extremely jerk move by shutting down the portal. I guess you can come up with an explanation for that, but let's admit: it happens so we have to sneak through the enemies that came to alive.

Thanks for your feedback! I agree with you re: that jump. Try as I might, I just couldn't make it any friendlier without breaking the rock puzzle :( If I ever re-master it, I'll definitely try to fix that issue.

(The portal shuts off because Dielya rescinds her blessing when she realizes you're a Thief. Sorry if this wasn't clear from the in-game text.)

Hey, no problem :) I slightly remembered/suspected there was an in-game text hint, just wasn't sure. The explanation - in terms of in-game lore - is perfectly fine, I like the fact that you did an extra effort and came up with something that made sense story wise. But here is something that may be worth to consider:

I think in normal cases - during a first walkthrough - players would probably leave the portal shut down when they enter the chamber of the hourglass (since in both cases of finally getting the two talismans the portal needs to be shut down as part of the puzzle). Players on the other hand - who think forward, or decide to re-play the mission - could choose to approach the final part of the mission in a different way by leaving the portal open and making the escape easier.
Don't get me wrong, I'm not suggesting you should change the mission (it's completely fine the way it is), my thought above just an idea you can consider when you (hopefully) decide to design future Thief fan missions. I think aspects like this are what can turn a mission into a really fun mission, Thief is an immersive sim after all, and the core concept of the genre is the way players can approach different problems in multiple ways :)