Normally, you'd only nuke if boss is under 30 minutes left.

However, with current event requiring as many RB spawns as possible, nuking is much more common and for good reason.

I personally am hitting Level 75+ bosses with a 5-rainbow squad for ~650k and 80+ with a 10-rainbow 2-squad for ~1.2M, unless it's already been hit by nukes and will clearly die long before it reaches 30 minutes.

I might try hitting one with my full 4-squad team just to see if I can kill a RB in one RP. 2-squad comes to ~1.2M, so I'd think anything under Level 80 would be dead meat.