Thanks, managed to get it working, although the solution is rather weird and doesn't make sense....
Like what the recommendations suggested in that link, I created a Compose:

I then converted the timezone and the weird thing here is that I'm using exactly the same source and destination timezone, which to me seems pointless because there's "no conversion" done essentially:

I then use that output for my end time for my Outlook automatic reply:

And that worked. However, it's pretty much the same result as what I had before, prior to all this timezone conversion stuff. If I take out the timezone conversion, the result is incorrect. If I change the source timezone to UTC+0, the result is also incorrect. So somehow, setting the exact same source timezone fixes the issue, which is weird. Oh well, it works.
I was also going to just change the time from e.g. 10:00 (10am) to 22:00, but I felt that it's a crappy solution.