The UI on the ignore feature is a little strange. When you enter the user name you need to press tab afterwards. You’ll then see the name in the box with a little x in a circle. Then you can select a timeframe and have it work.
Absent the little (x) you’ll get the defective error message that you need to select a timeframe, when in fact what you need to do is convert the letters “LSLGuy” into a reference to the user LSLGuy. For some totally dumb reason you also can’t use the standard @LSLGuy format. You need to type the letters and tab to “complete” the entry
I think the idea is that you can enter multiple names then ignore them all in one action. So they need some way to tell where one name ends and the next begins. The tab key is that way. And the (x) is the delete icon to remove an entry you no longer want.
Drove me nuts too until I figured it out.
See also Ludovic’s explanation a couple above your post. Same facts, different words. One or the other ought to click for you.