well what do you satisfy as enough risk? (how long is a piece of string)
Probably the only place that risks are assigned fixed values is in an SFEC. (That's more about how much money the CFS will spend in an area than anything else.)
Captains, Groupies & RO's are supposed to keep across the dynamic operational stuff in their areas - the variable factors like beginning & end of school holidays, weather, travel times, crew availability, gut feeling, etc. Then they decide how long their particular piece of string is on a given time & day. If it comes up short, they negotiate CoQ with the next layer up. They might get it, they might not. Depends on what else is happening, how good a case they can present, & how far up the food-chain it has to go for approval. Or at least, that's how the books of words indicate it is supposed to work.
Is that a long-winded enough non-answer ?