If you are 'Friends', i.e. have followed each other using the button on the top right their profiles, you can see their score on the quiz. Unfortunately, it is limited to the top 4 scores
(plus your own). It will show the amount of time taken to complete the quiz if they score 100%, otherwise it will just show the percentage only.
You can always check their "Stats" tab on the profile (second one along), and will tell you the percentage scored of any others you can't see from the quiz itself. There's no way to see the time taken on this however.
Best,
Hullabaloo