How to display posts of one category without dates?

either add a conditional statement to single.php, for the date output;
https://codex.www.ads-software.com/Function_Reference/in_category

or maybe use the css classes output by post_class() – if your theme uses that – in combination with some css in style.css;
https://codex.www.ads-software.com/Function_Reference/post_class

details depend on your theme

I hadn’t realized it was creating a special class, but it was.

<div id="post-145" class="post-145 post type-post status-publish format-standard hentry category-case">

“category-case” is the relevant class. All I have to do is

#leftColumn .category-case .info
	{
	display: none;
		}

and the problem is taken care of. Thanks for the suggestion.