I own a Canon 5D.Can the RS-80N3 remote switch hold open the shutter for long time exposures without having to put the camera in bulb mode? Because when you hold down the shutter release in bulb mode it activates the built in timer.I want to expose for hours not minutes.

I don't think you can do this without setting the camera to bulb. I'm guessing you have a time set on your remote. Zero out the time, and try again. You can use the remote as a regular shutter release, and lock the button down and let it sit for as long as you want. I used this feature a couple weeks ago to take some star trail photos.

If you know the exact exposure time you want to use, you can set the remote timer to hold the shutter open for that specific amount of time. In order to do this you have to have the camera set to bulb though.