That's a good idea. I just did a manual test, and noticed two things:
- Photoshop CC 2018 opens much faster than I remember Photoshop opening in the past.
- A screenshot saved as a file (Shift Command 4, by default) appears open in Photoshop as soon as Photoshop is fully active. So the OS deals with the delay.
Now, how would I create the step that opens a newly created file when I won't know its name?