BBT measuring on night shift?

Sara • River Ann born on August 9, 2017 at 5 lbs 13 ounces and 19.5 inches long ❤️ my world
So, I work night shifts as a pediatric nurse. On my days off, I have a normal schedule: wake up in the morning, go to bed at night. However, when I'm working, I got to bed in the morning and wake up at all different times. 
When should I measure my BBT?