Yes, holding in available in advance at certain locations.
In the app, if you tap the top-left button on the "Discover" tab, you can access the Filters. From there, under Seat Availability you can select the Date, Time, and Seat Availability you'd like for your future hold.
Tap the large button at the bottom to see all available workspaces with those parameters.
Then, when you click through to a workspace, you will see a large blue button at the bottom to place your future hold. To see all your holds, you can go to the "Seat" tab.