Try this:
Global number time_true = 0
+ Counter <= 0
+ Onscreen <= 0
-> Add dt to time_true
+ Else (in the latest beta)
-> Set time_true to 0
+ time_true >= 5
+ Trigger once
-> Do something
Basically this counts up time_true while the event is true, and resets to zero if the event is not true. Once the time_true reaches 5 (seconds), you can then run an event.