Giving proper notice. What would you do?

I have been a nurse for 27 years and have always given proper notice when I left a position. However, I signed on as a Resident Services Director for an assisted living facility about 3 months ago. Before I accepted the position I was told "what a contrast it was from long term care", "would be able to go home at night and actually have a life".

Nothing could be further from the truth! ALF is in fact much worse from a liablility standpoint for a nurse. I'm working 11 -12 hour days and usually get my first after hours calls within 3 blocks of the community when leaving. I have had 5 full days off in 3 months. I am dealing with a much less than professional or qualified staff than in LTC and I keep seeing my license flash before my eyes repeatedly. I was deceived into accepting this position. The wool was most definitely pulled over my eyes on this one.

I've decided to throw in the towel before I do in fact lose my license. The company I currently work for requires 3 weeks notice minimum for a person in my position. In my opinion I don't and won't need them as a reference with my extensive experience and long work history with former employers. I plan on returning to my previous employer. However, I do need to give some notice because ethically it is the right thing to do. Just can't justify the full 3 weeks. I was thinking more like days.

The question is: How much notice should I give? They advertised for literally months before I was suckered into accepting the position. I'm sure that they won't replace me in 3 weeks time. I'm ready to go NOW!