Big Pine,
It's doable. I live in Santa Monica and I have driven up and done Langley and come back in one day. I'm in pretty good shape and hiked TH to summit to TH in just under10 hours when the trail was virtually snow free. I did it via NAP which is a bit longer than OAP. I think OAP would make it a bit faster. This year the snowpack is pretty light and by early summer the days will be very long and the snowpack light. It took me 2hr45min to get to the trailhead from Santa Monica with one stop in Mojave. However when I did it I left in the dark when there was no traffic and I was driving well above speed limit.
When I did it, the whole trip probably took around 16 hours. 2hr45min there, 10 minutes to gear up, 10 hours to hike, 10 minutes to gear down, 2h45min back plus 10 minutes to grab food along the way and gas. Just comes down to your fitness...
Here's my strava:
https://www.strava.com/activities/1628329033
