Ok here's an example I hope its better explained this way.
Basically I made a global variable "WindTimer" and set it to 0 as my default.
System every 1.0 seconds I'm removing 1 from WindTimer
Also I set my timer thisway to prevent negatives
System WindTimer (les than or equal) 0 | Set WindTimer to 0
So lets say every 5 seconds I set my WindTimer to 8 (so that you will be recieving wind for 8 seconds
if my WindTimer is greater than 0 | apply force 200 at angle 180 at image point 0
I hope it answers your question. The Capx should be a bit clearer since you can see it in action.
 as a side note it probably would be wiser to change the 5 for a 10 and the 8 for a five so you don't have overlapping "perpetual" wind like in my capx