"Mark posts as read" options

[#1]

In My settings > Preferences > General > Mark posts as read I'm trying to opt for Automatically, after auto-mark period expires, but the period setting box is greyed out.

Is this a fault, or is the option permanently not available?

[#2 · Accepted solution]

I got the box to un-grey itself (purely by accident)

Just select the "Automatically, after auto-mark period expires" button.

Then click "Save Changes"

Now you can change the "Auto-mark period (Days)"

And "Save Changes" again

[#3]

Yay! Works fine now - thanks @SpendLessTime  

The fact that I was foxed and your discovery was by accident suggests that an explanatory note might be in order on that page.

Any PN staffers reading this?

[#4]

Yes the accident part was that I did the first click to select the option and than tab to go to the greyed out box. Tried to enter a number but failed. No surprise there.

As I moved my hand to the mouse, I accidentally hit the enter key which saved the change. And then I noted that the box was no longer greyed out.

If I hadn't tried to use the mouse but kept to keyboard navigation I wouldn't have found a solution.