There are 2 ways to refresh the Twitter Card. We did both of them and waited for 2days, and on the 3rd day, we could confirm that TwitterBot refreshed our Twitter Card Image on twitter.com.
2 ways to refresh theTwitter Card Image ( how to force cache purge of TwitterBot/1.0 )
In order to refresh the Twitter Card, Twitter says that we just add an extra parameter at the end of your image URL ( My Card information now refreshes, but images are not updating. How do I get the images to refresh? ).
And according to this page ( https://stackoverflow.com/questions/28207497/how-to-force-cache-purge-of-twitter-cards-bots ), we can update it by using Twitter Card Validator without adding an extra parameter.
If I do both of the 2 ways, how long must I wait for refreshing my Twitter Card Image?
We updated the Twitter Card Image of the "DomainBoard" on Dec 5, 2017. And we did the 2 ways above. And we can confirm that TwitterBot refreshed our Twitter Card Image on Dec 8, 2017.