Hey I have a skeleton with a lot of skins and most of them have their set of bones animated, So I guess there is no easy way to change the length at once right? I have to activate every skin select the timelines for that skin with box select and stretch or compress it.
Change Animation Length for All Skins
To change the length of an animation for all skins at once, you can follow these steps:
- Show All Bones/Slots: Press
ctrl+Hto ensure all bones and slots are visible. This will help you see all the keyframes in the dopesheet. - Show All Skin Attachments: In the tree properties, check
Show all skin attachments. This will display timelines for all attachments in all skins. - Select All Keyframes: Use a box selection to select all the keyframes in the dopesheet.
- Resize the Box: Once all keyframes are selected, you can resize the box to stretch or compress the animation length.
This method ensures that you are adjusting the animation length for all skins simultaneously without having to activate each skin individually.
For more detailed instructions, you can refer to the user guide on scaling keyframes in the dopesheet: Dopesheet - Spine User Guide: Scaling.
warmanw Sorry if I misunderstood the question, but if you want to be able to display all timelines of bones including skin bones and adjust the animation duration, you can do it by uncheck Hide viewport skin bones in the Tree view option. This may seem to only affect the viewport from the option name, but it also affects the rows shown in Dopesheet and the Graph view. When unchecked, you see the timeline for all bones, so you can adjust the duration by selecting keys.
OMG! I knew there was a way, I just lost that knowledge in front of my TV 
