Yes you can extend the timings of the missiles, but you should also consider the bigger picture.
When I made the AGM 129 (BVR missile) as someone requested I found that the actual missile had a range of some 3000 km's. I did extend the times etc. accordingly but what you then get is the missile lock on to anything inside the maximum range (you have no idea what you have locked onto!). if you then also fire the missile and if the timings and lifetime are set to accurate values the missile could still be flying off into the distance some 15 minutes later!
I did therfore put some more managable values in with comments in the readme file as to what to change if it did cause problems or if the values were to be modified etc.
<Gun>
           <Type>MissileLauncher</Type>
           <Name>AGM-129</Name>
           <Desc>Air Launch Cruise Missile</Desc>
           <HudString>AS</HudString>
           <Pix />
           <ConeAngle>0.005</ConeAngle>
           <TargetRange>3700000</TargetRange>
           <MinRange>2000</MinRange>
           <MaxGForce>2</MaxGForce>
           <Delay>0.0</Delay>
           <FxFire />
           <Sound name="..\..\..\Captain_Sim\Weapon\Sound\csweapon_rocket2.wav" gain="0.3" />
           <Shell>
               <Name>AGM-129</Name>
               <Desc>Air Launch Cruise Missile</Desc>
               <HudString>AGM-129</HudString>
               <Pix />
               <Container>CS_Weapon_AGM-129</Container>
               <FxWake>csweapon_rocket_wake2</FxWake>
               <Weight>1334</Weight>
               <TargetWeight>50000</TargetWeight>
               <Lifetime>30.0</Lifetime>
               <CtrLifetime>30.0</CtrLifetime>
               <Efficiency>1.0</Efficiency>
               <RadiusRatio>1.0</RadiusRatio>
               <DragCoeff>0.18</DragCoeff>
               <OpArea>0.015</OpArea>
               <GravCoeff>1.0</GravCoeff>
               <InitSpeed>0</InitSpeed>
               <EngThrust>15000</EngThrust>
               <ThrustDuration>5.0</ThrustDuration>
               <TurnRate>0.2</TurnRate>
               <SteerDelay>1.0</SteerDelay>
               <SeekerAngle>3.1416</SeekerAngle>
               <SelfDestrTime>20.0</SelfDestrTime>


These are the values I ended up with, I think you have to put certain limitations in place.

Pete