Should not spawn for a number of days. I know they can not be configured to spawn with a trigger like a quest (technically they can but it's too hard to code) so I would think that by day 50 the player may actually have a bunch of stuff ... The saw blades however should NEVER destroy blocks nor explode (why bother making creepers not destroy blocks )
Saw blades should be used only after about day 100.
Reduce the number of drones or their max life / damage