Keep on reading for 15 minutes:
From Trust Level 1 (Basic User) Requirements :
Note: The read time you see in your profile is an approximation. For example, you might think you’ve reached a read time of 1 hour, but in reality, your read time might be more than 45 minutes, but less than 1 hour.
A way to access your profile is by clicking on your icon to the left:
Then click again:
And now you see the ‘1h read time’
Maybe these screenshots can be added in the instructions for extra clarity, or is this overkill?