The Nikon D5500 is supported by SGP. When you choose the camera type select Nikon. There is a box to the right of Nikon that says Settings. Click on it and select your model. You will see the D5500 there as a choice.
Also I think on the camera you select Manual and then set Bulb - at least I do that with my D5100.. It should work ok - if you've tried this and you still have an issue let us know.