nerding out about D&D
okay so working backwards from CR, I get a vague average of PCs doing 2.8-5 hp/round or 11.2-20 hp/round damage. It'll vary with AC and resistances which change PC chances of damage. (It also seems light.)
And I figure 12 minutes to adjudicate a single round of combat isn't terrible, since that means in an hour a 3-5 player group can resolve about 4 rounds of combat.
So assuming I want the monster(s) to last >1 round so everyone gets to participate (including a chance to appreciate how badass the monster is), but <10 rounds so players get to do