If the true respawn is set to 24 hrs, I previously uncovered evidence that Scott Charisa is indeed on basically an 11hr30min timer with +/- 30 mins.
https://www.project1999.com/forums/s...d.php?t=281965
If that is to be believed, I also found evidence that every mob in EQ with a spawn time over 2hrs had a variance. Post here:
https://www.project1999.com/forums/s...7&postcount=26
They mention the variance modifier is percentage based, so if evidence on the variance is lacking, safer to assume doubling the scout variance (so +/- 1hr would be my suggestion).
There are definitely exceptions to this such as skipping spawn cycles to extend variance, but without that evidence I say the +/- 1hr is good, or at least a happy compromise.