Dragging the End Time Bar is too time consuming - Need a workaround

There's may be a bug in Storyline so that when I open an existing course and edit certain slides, every slide I edit gets its Total Display Time increased to 15 minutes - much longer than it was before. I believe it may be because my original audio clip was 15 min but I trimmed it down and was hoping there would be an easy way to get the end time to align with the newly edited audio to match the other end times of my other assets. 

Question: how do I set the Total Display Time for a slide, other than going to the timeline and dragging it back to where it was before?  It's very time consuming because I can only drag it about 30 seconds at a time, then click the scroll bar at the bottom, then drag some more.  And repeat for every edited slide...and sometimes it messes up and I have to start over. Is there a way to just edit slide end time? 

Thank you for any help in advance.