If the shot can’t be done at the pre-planned time, what one would do depends on a few things.
Let’s say one of the star shots was delayed by 1 minute due to something simple like sextant or mount issues. If using MOO and MOB, the multiplier is the number of minutes before or after the fix time. So, let’s say we delayed the first shot by 1 minute – so instead of multiplying the MOO+MOB corrections by +8, we would multiply by +7. We are, in effect, advancing the LOP by slightly less than was originally planned.
Note that the multiplier changes to negative if the shot occurs *after* the fix time.
This works, of course, for non-integer minutes – say instead we delayed the first shot by 30 seconds: then the multiplier would be +7.5
This change to the multiplier can be handled very quickly once the Nav gets back to his station.
I’m not sure what duration you imply by “consistently can’t be obtained” – if the sky is obscured and you can’t climb above it, your dead reckoning skills will have to do. You can bet that the crew will be looking for stars out the windows and if one appears they will get the Nav on it quickly and then take a shot at the fleeting target. On something as unstable as an aircraft, the averager will get better results, but if all the Nav has is a fleeting view, he/she will be prepared to take a snapshot and record the time. He may not even know what star it was, but from the Veeder-Root counter (bearing), recorded altitude, and a 2102-D star finder more likely than not he will be able to figure it out. The reduction would then follow nautical practice.