Great

Then the work was worth it and I can keep this as an official new feature.
That means that the version check took 85 seconds for you, so a total of 6 passes were required. Since each pass always costs an extra second because of the automatic refresh of the page, the bottom line is 79 seconds. That also means that my previous estimate/calculation was far too optimistic and phpBB can actually determine far less than 66% of the versions. Purely mathematically only ~38% in your case. But as I said, these are all just estimates and always depend on the 3 factors mentioned.
In the meantime, I have already started with b3, which has fixes and improvements for the new version check of b2. In addition, extensions from the CDB are now clearly marked as such in ExtMgr and the corresponding CDB page can now be called up directly on the "Details" page for each extension. As soon as I have published b3, I will announce it here in this topic.
May the backup be with you. Always.