Classic transition is to stick with 12 hours and eliminate any snacking - just three meals. When that’s not a challenge (which may be immediately) go to 14 hours. Progress to 16 when 14 is easy. Move on to 18, then 20. When 20 feels ok try OMAD. If it’s too stressful you can always skip back down a rung.
Keep your calories in the eating windows to your TDEE at the beginning, and cut from them, from 100 to 500 below. Avoid going below 1200 calories a day. Try to make sure you’re getting good nutrients in during your eating windows. Use water, black coffee and tea to keep you going during your non-eating hours.
Best of luck - you’ve got this!