We did a version of this trail (https://www.alltrails.com/trail/us/california/mitchell-creek-to-diablo-summit) but added on North Peak (by accident) whoops, and the Mount Diablo summit. Beware that if you want to hit the summit of mount diablo, you must deviate from the red path marked on the all trails map.

Choosing to follow the first half of the trail up the beautiful ridge line through Eagle Peak was a great choice. Be careful with the navigation at the turnout for North Peak and Diablo Peak. Once you reach the summit of Diablo, the decent largely takes place on a fire road/wide path.  There were a number of mountain bikers (we wished we had our bikes) on this section.  Our total hike time was ~7 hours including breaks.

We heard the terrifying sounds of a mountain lion below!