So giving 24 hours of darkness doesn't really do anything. I've tried it on a couple grows and noticed no difference in how the plants flower. As far as dos and don'ts go, there really aren't any. You can just cut back on the hours of light either from lights on, lights off, or both.
In your situation, if I was you, I would just set my timer to 8am-8pm which would be right in the middle of your current light cycle making things nice and easy.
There's really no need to overcomplicate this step despite all the information and crazy ideas out there about all sorts of different growing techniques. To be honest, most of the information out there is untested nonsense that people repeat and spout as if it was a scientific fact. Keep it easy and simple and you really can't go wrong.
Hope this helps! If you need any more help or just want to chat, feel free to dm me!