So is NIP-46 like a one time password?
Discussion
No, it's a protocol, how apps can talk to your keys.
Okay, but can we say the protocol involves the generation of a one time string? Or can the bunker url be reused?
It involves generation of session keys by the app, and use of those temporary keys to talk to the signer (nsec.app) over some relay.
Bunker url is just a pointer to your npub and a relay over which app can talk to signer. But bunker url can also contain secret that has pre-approved permissions attached to it by the signer. Nsec.app doesn't support that atm.