There is no straight forward answer...

Unions typically - anything over 8 hours a day is OT. My experience:

UAW - 1.5 times over 8 hours/day. 1.5 times Saturday.

AFL/CIO (laborer's) - New construction -2 times over 8 hours/day. 2x Saturday and Sunday. Renovation work - all ot is 1.5x - after 8 hrs/day and sat/sun.

IBEW - 1.5x after 8 hours. 1.5x first rest day. 2x second rest day if ya worked first rest day.

As an exempt engineer - I got 1.5x over 40 hours in Toledo. I got 1x over 40 hours in Miami. I got zip in Houston. I do get 1x comp time at NASA now.

Tom