ORIGINAL: TheOriginalOverlord
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I'm going off what I read here..
http://www.allworldwars.com/Finding-Fixing-Finishing-Guideline.html
The plotting officer would manually update the plotting board in the control van, while at the same time the battalion commander was attempting to acquire the track using the co-located Spoon Rest radar. Once the track was detected, the battalion could transmit from the Fan Song and attempt to acquire the target and begin the engagement process.[18] When the battalion operated without the aid of acquisition radar, or was cut-off from IADS cueing, it could still self-acquire using the Fan Song, but this was a degraded (autonomous) mode of operation. By 1965 the tracking process, from initial EW detection to Fan Song handoff, was completed in less than 5 minutes.[19]
The SA-2 battalion would transmit using the Fan Song in an attempt to acquire the target. The process of acquisition, target tracking and missile launch took approximately 75 seconds.[20]
I understand what you are saying about the scope of the game... as a "player" I'd personally like to be able to shoot at FCR radars while they are still in "acquisition" mode...instead of having to wait until a missile(s) is in the air. JMHO
The same web is in later part saying that later it was reduced to 30 seconds.
Technically SA-2 doesn't need to activate radar at all for missile firings as it can use dog house or carat camera (in later versions) for target track. The number of 75 seconds corresponds to at that time procedures based on at that time crew proficiency.