By default, the duration of a Campaign is set to 30 seconds, but you can easily make the campaign length shorter or longer depending on your needs.
Create a new Campaign or edit an existing one. Scroll down to the Timeline section.
Update the timeline length with one of the following methods:
Automatic Duration: When this option is selected, adding new items to the timeline will expand it automatically. As you remove files, it will shrink as well. Meaning, the timeline will always have the same length as your content.
Manual Duration: Change the number next to the clock icon on the Timeline header. Note that the duration is written in seconds, so if you want a three minute campaign you need to type in 180. Once you hit enter, the timeline length will match the campaign duration.
Variable Duration: When the duration set to variable, one timeline has to be the main timeline on which the other timelines are oriented.
Use the bar on the bottom of the Timeline to scroll through the ruler.