Basically, you can do what you want and you will get away with it until there is a serious incident/accident. Then, upon investigation by the regulator, will your actions leading up to signing on for the TOD will be investigated. YOUR legal responsibilities with regards to rest and fatigue be examined. YOUR decisions will be challenged and it will be up to YOU to defend your actions and prove that you were not negligent. The company will absolve themselves of any responsibly . The regulator will need someone to blame. The only one who can manage fatigue and rest is the individual and only they can determine if they can legally sign on for duty. This is the world we live in now.
If I had a 20+ hour TOD ahead of me there is zero chance I would commute over the day of departure.