I know a lot of retired Naval officers (I'm almost there myself) that have done well investing who also have wifes that work. They want flexible hours, stress free...they all have done well in their first careers and have no ego invested in the next stage of their lives. They also have excellent retirements and health care.
One works at the local Lowes. The pay is good and his hours are exactly as the ones you want. He loves the job.
Another is a car nut who works at an independent foreign auto repair shop. They allow him all the flexibility he needs...there is evidentially a real shortage of reliable, mature mechs who know what they are doing.
The are a lot of defense contractor in my area that support less than full time employees with certain skills: proposal reviews, contracting experience, etc. Check out the local defense contracting firms that provide support to the military. A very good friend of mine works 30 hours a week doing this.
Most of the rest work in areas that would not fit your daily schedule. All the best.