What I have done in the past is set my home thermostat to 83 and did not have anyone turn on UVB basking bulbs. Thats was for my own state of mind because I feared they would forget to turn them of at night.
You can buy a timer to turn monsters lights on and off, I would do several test runs.
Your sister can offer fresh food either early in the morning or after dark once hes asleep.
A healthy ig can survive without UVB for a week or so but I wouldnt keep him in the dark or lower temps than 80.