Multi Timer is simply the best timer and stopwatch app for Pebble.
You can create as many independent timers and stopwatches as you need.
With the release of 3.0, timers will now launch the app when they finish, meaning you can quit Multi Timer while timers are running and still be notified.
The recommended method for downloading Multi Timer is to use the Pebble appstore on your Android or iOS device.
You can also download the PBW file directly from GitHub.