Made a simple .sqs file, could make a .sqf, but since I'm slower with that...
This script is so simple that .sqf won't make a performance difference anyway.
An object called speaker (in my mission a roadcone).
A gameLogic called attackcenter.
A Radio alpha trigger that sets varable IDFattack to "true".
If you want to alter the "area size" being attacked, just change the "+ 50 - random 100" numbers to i.e "+ 500 - random 1000".init.sqs
 exec "IDF.sqs"IDF.sqs
speaker say "IDFalarm"
? ! (isServer) : IDFattack = false; goto "start"
_attacklength = 60 + random 240
_time = 0
? _time >= _attacklength : goto "end"
_delay = 5 + random 5
_boom = "Sh_120_HE" createVehicle [(getpos attackcenter select 0) + 50 - random 100,(getpos attackcenter select 1) + 50 - random 100, 50]
_time = _time + _delay
IDFattack = false
Use the trigger and see the effect. If you really want to have random attack times all through the day you could easily accomplish that with a looping script that sets IDFattack = true at random times. Don't forget to use publicVariable if you want it to work in MP.
Since I don't have a sound called "IDFalarm" you get an error message, but I hope you know how to define sounds in .ext and sound folder.
Example mission included.
Hope it's good enough