We Never See Nothing

I read in internet that for each 24 words seed someone or a computer guess, it needs to: generate a private key AND a public key to check whether addresses generated from that 24 words seed has any unspent bitcoin/crypto associated with.

I think private and public keys are generated automatically when a 24 words seed is entered into a hardware or software wallet.

So my questions:

1- is speed of private and public keys generation dependent on the computer that is trying to brute force, or it is a fixed speed or something dependent on blockchain speed?

2- how long this private and public keys generation after each 24 words seed guess can practically slow down the brute force?