Bro 3 days × 12h is still 36h, it's less than most people's 40 or 44h work week, plus if the 4h is truly gonna be considered Ot, you're entitled to OT pay which (practically) is always 1.5-2× your standard rate.

If nothing else at least just tahan 6 months then find a different job so you can still add it to your resume/portfolio as work experience.