By itself, I thought this was okay. Telling me you normally run a longer program but cut it down to 4 hours for this event makes sense. This event didn’t have a 6-8 hour session block for you, and it was feasible for you to provide a valuable session in 4 hours while using content from your longer program.
The wrinkle comes when you don’t actually modify your program, but instead decide to simply drop some chunks out. Then, you use your original slide deck with slides that you gloss over, because of time.
The problem I see is when you gloss over a slide with applicable content, or an exercise that looks valuable. It feels confusing to have slides included that aren’t used, and even more so to see an exercise that might be either interesting or valuable (or both!) and hear, “we’ll skip this slide due to time”.
Certainly there are times you must cut content because of discussion or something else changes, and that can be okay. But leaving those slides in your 4-hour version slide deck just feels lazy.
Whether the session is 8-hours, 4-hours or 17 minutes I want to feel like I’m getting the whole thing. Take the time to prepare for the duration of your session, and make your audience feel like they’re getting their money’s worth, no matter what the duration.