If steam version go to: C:\Program Files (x86)\Steam\steamapps\common\911 First Responders\Mods\Los Angeles Mod v2.1\Specs where ever you have the game installed, in there look for these files fp_params_challenge fp_params_endless and you can set the calls 0 = off and 1=on also
TO edit files use notepad or notepad++ just right click the files you want to edit and click edit
you can change this to if you want:
<MinDurationBetweenEvents value = "350" /> SET THIS HIGHER if you want calls to come in slower
<MaxIdleDuration value = "100.0" /> SET THIS HIGHER to
<Seed value="0"/>
<BuyFactor value="10.0"/>
<SellFactor value="0.5"/>
<GlobalEventFrequencyFactor value="1.0"/>
<TimeSpeedFactor value="0.0"/>
<StartBudget value="1500000"/>
<MaxBudget value="500000"/>
<Earnings value="5000000"/>
<SquadPriceGrowth value="30.0"/>
<MaxParkingSpace value="150" />
<InitialEventFrequencyBoost value="100000.0"/>
<InitialEventWaitDuration value="400.0"/>
<starttime value="13:00"/> THIS is the time of the day
Hope this helps