oof
5 characters takes about 4-7 days
each character has a factor of cost of extra time that i have not actually measured, it's probably a power of 1000 or something, i dunno
put it this way, i'd estimate 6 characters will take a - 6 core, 12 therad AMD 4k series CPU about 2 weeks and 7 will cost you 3 months and 8 will cost you over 6 months
it's bound by the amount of computation involved in deriving a public key from a secret key using secp256k1 and this is possibly one of the most expensive computations that is considered "normal" at this time in computer science history