Make objects NOT default to "Show until End" OR editing the timing of groups

Hi, Carter.

While not currently a feature in Storyline, we have a feature request logged to change the default setting 'Show until the end of the timeline' when inserting objects.

I will update this discussion if I have any news to share or if this request makes it to our feature roadmap. 

In the meantime, you can adjust the time of multiple objects on the timeline by selecting them with CTRL:

You can do the same with objects within a group:

I hope this helps!