I ran Tor nodes, had a bunch of blacklisted IPs, and just stopped running them and it was fine? Blacklisting Tor nodes requires updating the data often, so it falls off pretty quickly. To discard an entire /24 would be pretty funny over that!

Most people just use a DNSBL to block Tor exit nodes. They're pretty trivial to find online and presumably, very easy to set up because the list of Tor exit nodes is publicly available.

This also means the expiry time is usually tied to however long a Tor exit node stays on the DNSBL + 3 or so days (depends on how long the software is configured, but 3 days is typically the assumed default for IPs that tend to get mixed up with automated spam, of which Tor is also a massive purveyor.)

It's recommended to put an exit node on its own dedicated IP address.