Hey,
Try this:
1. Find your level's STL file and open it in a text editor.
2. Scroll to the top, and find your first sector. It should look something like this:
- {l Code}: {l Select All Code}
(sector
(name "main")
(music "music/chipdisko.ogg")
(ambient-light 1 1 1)
(background
(speed 0.5)
(image "images/background/semi_arctic.jpg")
)
(camera
(mode "normal")
)
3. Insert the following code after it:
- {l Code}: {l Select All Code}
(leveltime
(time 20)
)
with the time being the amount of time you want on the clock.
4. A clock should appear in the editor(like your screenshot) with the time you set on it.
Hope that helps!