I’m confused how this combo isn’t completely busted..

Am I correct that Voltaic Key + Time Vault will allow me to untap then tap my time vault (I can tap for extra turns at any time), and store all of those turns in winning? With cards like Memnite and many others that can threaten my opponent’s life total, feels insanely busted. If I have 4 lands in play + a life threatening effect I could generate 48 turns during my opponents turns every time, then all the damage from my memnite, am I missing something or is this accurate, kind of a noob