Adventure Time started as an animated show, not a comic. The TV series gained popularity before any comic adaptations were made. The animation was the initial form of the story's presentation to the audience.
Adventure Time has been at Comic Con on certain occasions. Usually, it's part of the event when there's new content or special announcements related to the show.
The Adventure Time comic is canon. It adds depth and new perspectives to the existing storyline, while adhering to the fundamental framework and lore of the franchise.
One way to show time passing in a comic is through the progression of events. For example, if a character starts as a beginner and later becomes an expert, that shows time has passed. Another method is to have visual cues like faded or aged objects. You could also incorporate time stamps or calendars in the background.
The Witcher originated as regular novels. But due to its popularity, comic book versions were also created to offer different ways of experiencing the story. So, it's both, depending on what you consider first or prefer.