i have a sharepoint 2013 project site (connected to an instance of Project Web App). on my site homepage, i am displaying the default 'task' web part WITHOUT the timeline. i then added a timeline web part manually (because i needed to display it on a different part of the page) and connected it to the task list on the site. Now, when i select an item from the task list web part on the homepage and click 'tasks' in the ribbon, 'add to timeline' is grayed out. if i go to the actual task list and select an item, i am able to add it to the timeline via the ribbon. 

is it possible to add tasks to the timeline (separate timeline web part, connected to task list via 'web part properties) from the site homepage? or is it only possible if you first go to the 'tasks' list page?

thanks so much in advance for any assistance! it is much appreciated!

Try below:

http://itfreesupport.com/2015/06/sharepoint-add-to-timeline-option-is-disabledgrayed-out-on-project-site/