Longest-time-verifying block I heard that there was an old block with one transaction and it takes 20 seconds of CPU time to verify.

1) Which block was it? I forgot its block height.

2) Is there a block that takes more time to verify? Or is there a similar block?
I'm not completely sure if this is what you are looking for, but it may be.

Here you have a type of transaction that takes 3 minutes to verify, and that was reported back in 2013. (CVE-2013-2292). Moreover, in Sergio Demian Lener's blog you can find a related topic, where he explains how he found a vulnerability that used the FindAndDelete function and OP_CODESEPARATOR to create a transaction that toke up more than 5 hours to verify.