The clock timer can be spawned using F11; I just copied the script in notepad from bedroom, pasted it into my map, and moved the objects ingame.
The mirror can be done with QuArK, but I am not really sure how to do this. I think you have to create a mirror and link it to a specific face. There should be tutorials for this however. An easier way would be to just copy the mirror that already exists (forgot who made it), paste it into yours, and position in with F11.
You can easily make see through one-way walls by using the NULL texture which should be included with QuArK. If you don't have it, all of my maps do so you can just copy it. If you use the NULL texture on a face it will make it see through but it will still have collision properties, and if the other side has a texture then it becomes a one-way wall.
Hope that helps