I tried one of the older, shorter .onion addresses once out of interest. Didn't take long on a laptop to get a specified 7 characters at the beginning.

I don't know how much the longer .onions affects generation time - anyone?

Is there a script to do that or did you roll your own?

I used https://github.com/katmagic/Shallot back then and it took 35221958203 attempts to find one with my chosen seven characters.

For the longer v3 .onions you'll want a different tool, this page mentions some and makes some estimates for finding increasing lengths of characters: https://www.jamieweb.net/blog/onionv3-vanity-address/