Here you go!
500/30=16.7, or 16 rounding badly.
So at full health and dealing 30 damage each time, it would take 16.7 hits to kill a player.
At the Destroyer's health of 60,000, it would take 3,529 hits at 30 damage to kill him.
At 1 stab a second, that's 3,529 seconds, 58.8 mins, or 1 hr...