To have the Timelapse+ measure the Bulb Offset, you'll want a cable like this:

It goes from the camera's PC (flash sync) port to the AUX port (upper right) on the Timelapse+.  Then, connect the shutter adaptor cable (C3) from the upper left port on the Timelapse+ to the camera.

You'll then be able to use the Timelapse+ to measure the Bulb Offset.

But, that said, a simpler way might be like this, since it doesn't require any extra cables:

With the camera on a tripod in manual mode, set the shutter speed to 1/10 second and the aperture and ISO to whatever is needed for a good exposure.

Then, switch the camera to Bulb mode, making sure the ISO and aperture are still the same.  On the Timelapse+, go to Timelapse and set the mode to 'Bulb Photo', then set Tv to '1/10' and press the upper right button (start).

Then, compare the two photos.  If the Bulb mode photo is brighter, the Bulb Offset needs to be decreased.  If the Bulb mode photo is darker, the Bulb Offset need to be increased.  Continue until the bulb photo and manual photos match.  Be sure to use the camera's histogram view for a more accurate comparison.