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So I have a large project with many layers. It's 30 seconds long. I want to save it as a new project, but I only need 5 seconds of that project for this new version. I need all the layers though. So how do I easily delete everything but the five seconds I need for this version, and on all layers? I can do it manually, one layer at a time, but that's really tedious because I have to select the region before or after in a 30 second timeline for each and every layer and that is fiddly. Is there an easier way?

This might work for you:

Duplicate the Project. Select All Layers. Adjust the timeline by dragging the last image back to the desired endpoint. The Shrink/Cut Images dialog box will automatically pop up (when the dialog box appears, the timeline will "jump" back to its original length until you hit apply). Select "Cut Images" and it will apply to all layers selected.
You can make adjustments to one region at a time. If the desired segment is in the middle of the entire sequence you'd have to adjust the portion in front and behind separately. So at most you'll have two steps for all layers (but not each layer separately).

The problem is, that only works if all your layers are all the exact same length on the timeline. Otherwise, it ruins the layers I want maintained. Here's an example of that not working.

Create a button with one action line in it: Set KeyStroke to Project:Clip:Delete Image
Working on a copy of the project (obviously)...
Select the frames you intend to delete, on one of the layers that is the length of your project
Press the new button
Bang, done.

Ah, that's interesting because it does it on all the layers prior to the area I want to save, but after the sequence, the button only does it to the one layer. I wonder why. At least it helps, but if you know why, do let me know.

Also worth noting, any layers which are a held BG, just disappear completely. Ideally they would not do that, but I can't see any way to avoid it apart from dragging the instance over to where it needs to remain.

Seems to work for every situation I set up... Can you show example of how it fails?

What happens if you insert a new layer 0 which is the full length of the clip, then select the frames to delete on that layer?

Here's a movie I made where I deleted from a layer which had instances from beginning to end. See the strange behaviour on the other layers? (Sorry, I don't know how to make the movie appear in this message directly, so it's a small download.)

Could you please try creating a NEW LAYER ZERO (TOP LAYER above all others) that is the full-frame-length of the clip (extending beyond the final frame in all other layers)?
Then, after making all the NEW LAYER'S frames into instances, select in the NEW LAYER the frames you want to uniformly delete from all other layers... then push your new button.
Finally, kill what remains of the NEW LAYER.

In tests I found that works every time... and I also found if you use any other than the ZERO layer to select the frames, strange results can sometimes happen... leading me to believe that the Project:Clip:Delete Image command works from the TOP layer, DOWN. Perhaps some other forum users could confirm the behavior.

One other thing I found... If any lower layer has first-to-last frames which are completely contained inside the TOP LAYER'S selected frame range, that entire layer is removed, which makes sense I guess...

I can't think of anything else to suggest.

maybe i'm missing a point but you can do this very easy...
by splitting the project and deleting the unwanted bits

in these cases i split the clip at the desired spots.
so if i want the middle bit...i do "splitclip" at the first frame i want to keep
and then in that newly formed second clip i go to the first frame i dont want and again do " splitclip"

now i have three clips in the project view and i delete clip 1 and 3....
leaving me with one clip of the desired framerange and with all the layers of the original.

Svangali, that worked perfectly. Thank you!!

Peter, that is absolutely a logical way to do it as well, which I had not thought of. Okay, then problem solved too ways. Many thanks!!