I can open two projects, but not two timelines

In the Productions workflow, you can have multiple project windows open in the Production panel. I'm a single-person shop, but I've found this is an awesome way for me to work, as all my b-roll, audio, template projects are available for use in any other project.

The first of my links gives the basic look at this, the second includes more working specifics including a link to a pretty decent reference manual.

And ... this is very different. You create a Productions folder on-disc, then in Premiere, "New Production" choosing that folder to house the production. Create additional subfolders for various sections of that project, OR ... as I'm doing, subfolders for my main areas of jobs, then within those subfolders, further ones for each job.

Within those subfolders, you make new project files for each part of a project. They even suggest one way of looking at this where you use project files to hold say the media that you would have used a bin for.

You can grab any asset from any project within a production, and use it in another project ... and there are no duplication of assets from project to project, it all loads much faster, and it's pretty slick.

Neil

Premiere Pro Productions Introduction

Using Productions in Premiere Pro

You cannot have two project windows open at the same time. You can open two timelines (pancake as Neil already explained).

You can have a timeline panel open showing in the Program monitor. Select the other sequence in the bin, right-click, open r sequence in the Source monitor. In the source monitor's "wrench" icon menu, tell it to open the sequence in the timeline.

Now ... click on on of the sequence names in the timeline panel, and drag it down just a bit, until a blue bar appears under it across that panel. Let go and it creates another timeline panel for that sequence. This puts you in "pancake" editing mode, with one sequence in the Source monitor, one in the Program monitor. I've got an example below.

And of course you can search here and elsewhere for "pancake editing" in Premiere.

Neil