Hi Dave,
You may be looking for “Sequences”. You can have multiple timelines (Sequences) open at once in Premiere, and can Copy/Paste groups of clips between them. For instance, you might want to break up your long video into several shorter “subjects”, so each subject can be worked on it its own Sequence independently.
Just go to File > New > Sequence to create additional Sequences, and each of these can be renamed as well to stay organized.
Note that for larger projects, it can help to not keep multiple Sequences open at once, if it is affecting performance. They can be closed, and will reside in the Bin until re-opened. Can be helpful to close extra Sequences, then Save, before exiting Premiere, otherwise it can cause Premiere to take a long time to open if many complex Sequences are open.
Jeff Pulera
Safe Harbor Computers