Board Thread:Support Requests - Getting Technical/@comment-30702882-20190804005127/@comment-34888194-20190804020223

Autoblocks only last for 24 hours. So even if you block someone's last IP, their IP is blocked in a fixed time of 24 hours, regardless of how long you blocked the account. So even if you blocked the account for like 2 hours, their last IP is still blocked until 24 hours has passed since the starting of the block. But it's always better to block someone's last IP since it slows them down from creating alternate accounts.

Blocking an anon is different. Their block last depending on how long you block an anon user.