Holding a tiller And a spotlight at the same time is a pain. I want to rig up a small light bar for solo hunts. Question is, how long will a small 8-12 inch led bar last on a fully charged boat battery. The only thing the battery will be for is my bilge pump, red/green and white lights and the light bar. I'll only need it for the run to my spot in the dark, which won't be too far. Or does anyone have a better light suggestion.

I run 2 7" Cree light bars and everything else you described on one battery, also used as my cranking battery. I have always just ran one battery and never had an issue. One night I went bowfishing and ran the led's for 4 hours and motor cranked right up when we were done.
You will be fine, the led's do not draw much power at all.