There is a reason why the D&D 5e creatures have their HP written in dice values (4d6+10).

It allows for variation within the stat block. But it also gives a maximum and a minimum HP they can have.

Most of the time you use the average. But if the game is too slow, you can lower it to the minimum HP. And if they are steamrolling an encounter, you can just increase the HP to the maximum.

This makes encounters more dramatic and fun.