Update Content For Thoroughness
In short, your content should be updated to make it as complete and as thorough as possible. If new developments in the topic arise, or the original post didn’t fully address all sub-topics related to that top level topic, then it should be updated when you have more resources.
Update Content For Seasonality
Certainly, any content that is seasonal in nature should be updated periodically, like if you’re discussing summer fashion in 2021 those fashions won’t be the same in summer 2022.
Update Content With New Conversations & Feedback
Often when content is published, you hopefully will be posting on social outlets and channels and aiming to get conversations going on the subject. If those posts gain some great quotes, or generate meaningful feedback, you should update the post possibly even embedding tweets or block quotes attributing those further ideas.
Evergreen Content Is The Goal
The job’s never really done. If you’ve done your basic legwork to turn “one-time content” into a post that can “stand the test of time”, there may still be developments that occur or just new viewpoints of your own that you want to add over-time. It’s worth it to revisit content on a consistent basis if you’re making edits and additions. So something like a revisit anywhere in the 1-6 month range will always “bear fruit”, especially if you’re coming back to add missing internal links or using new keyword research data.