Here's a way:
Make an entity and set it up to spawn when activated and also make it an "IsObjective" (Make sure there are NO OTHER OBJECTIVES IN THE LEVEL)
Give it this script for it's appear script:
:state=0:entityaddhealth=-9999
That will cause it "die" the moment it's activated, completing the objective and finishing the level.
Now, simply make a triggerzone, put the entity's name in it's IfUsed field, and give it this script for it's Main script:
:state=0,plrwithinzone=1:timerstart,state=1
:state=1,timergreater=10000:activeifused=1
Now, when you enter the triggerzone, the level will end in 10 seconds.
The one and only,