Tim Hunt

I think Yes and Yes.

The could be developed as a quiz access rule plugin. https://docs.moodle.org/dev/Quiz_access_rules

You can get an initial indication of where the time is being spent using the Developer tools in your web browser. The Network tab will show you what is loading, and how long each thing takes. (However, my guess would be that it is processattempt.php.)

Turning on Moodle's option to display performance info in the page footer (https://docs.moodle.org/311/en/Debugging#Performance_info) can also give some clues.

To drill down into even more detail, you really need a PHP profiling tool (e.g. Tideways - https://docs.moodle.org/dev/Profiling_PHP).

As far as I can see, no-one has actually reported this properly. I have now created MDLSITE-6552, so hopefully this will get fixed.

Don't be afraid to try this out (e.g. at https://qa.moodledemo.net if you don't have a test Moodle of your own that you can use). In this case, experimenting yourself would probably have been quicker than waiting for someone else to answer.

I'm pretty sure that it works the way you want.