Niko on 27 Aug, 2015 02:23 PM
Please try this first:
Delete it from your "Applications" folder and empty the Trash.
Then download it from the App Store again.
If this doesn't help, I'll need the system log that is generated after you try to launch Timelime.
You'll find the log in the Console app. This app is located in the folder "Applications" > "Utilities". If you need help with this, let me know.