Open the composition you want to resize, then click Fit comp. Snippy finds the earliest layer in point and latest layer out point, and makes the composition that long. It resets the work area to cover the full result.
Fit comp always uses every layer in the active composition, including locked, disabled, and guide layers. Your selection does not limit it. A long background or guide layer can therefore keep the comp long.
Keep the existing timecode
By default, Snippy moves all layers together so the earliest in point is at the beginning of the resized comp. It also adjusts the comp’s display start time to preserve the content’s displayed timecode. Comp markers move with the layers. Locked layers move too and keep their locked state afterward.
For example, start with a 10-second comp whose display starts at zero. If its layers span 1 to 6 seconds, Fit comp makes a 5-second comp. The layers occupy relative times 0 to 5 seconds, while the displayed comp start becomes 1 second. Their displayed timecode is preserved.
Relative layer spacing stays the same. The playhead follows the shift where possible and stays inside the resulting composition.
Start content at relative time zero
Shift-click Fit comp to leave the existing display start time unchanged. In the same example, the content and displayed timecode now begin at zero.
If the composition already has a nonzero display start time, Shift-click keeps that value. It does not reset the display start to literal zero. The content begins at relative comp time zero.
The Fit comp moves content to 0 setting makes this the default. Shift-click always reverses that setting for one action.
Check the result
The message Comp fit to reports the new duration. timecode kept or content at 0 appears when the layer timing was shifted. If the timing already fits, Snippy reports no change.
The comp has no layers means there are no boundaries to use. Add layers first. Fit comp changes duration and timing only, so the composition’s pixel dimensions stay the same. It does not trim layers inside nested precomps.