If in runtime:
Write new simple actor, in PostBeginPlay in that actor SetTimer( 10.0, False, 'Destroy' ); - collision set to block all.
Now you need figure out when and where spawn that actor.
Write new simple actor, set collision to touch all and use function Touch to switch collision to block all. But before switching delay that event for i.e. 1 sec. After that set timer for 10 sec to switch back to touch all.
Now you can put it in to level.