Time limit for NCAA field goals?

[jchamp]

Originally Posted by voiceoflg

Maybe a silly question but why not use the actual time from when the ball is snapped until the time the ball crosses the crossbar or goes OOB?

We're not playing Madden 20-whatever. So the clock operator doesn't have an electrical signal to know when the precise moment is that he should flip the switch.
Even though it's not codified, it's good to know, for strategic planning at a part of the game when literally, every second counts, what expectations exist. It's well known that a second or two will tick off the clock when a dead ball occurs due to an incomplete pass, score, etc. occurs. And "normal" field goals do have a predictable flight time.
If the losing coach sees that 46 seconds are on the clock when the 3rd down play ends, he can expect to receive a kickoff. With 45 seconds, he knows to take risks on the field goal... and all those other minutia.