Question

I usually work/works for 6 hours a day​

Answer 1

i usually work for 6 hours a day

Answer 2

If you're referring to your own work schedule, you can say, "I usually work for 6 hours a day." This indicates that you typically dedicate six hours to your work on a daily basis.

Alternatively, if you're referring to someone else's work schedule, you can say, "He/she usually works for 6 hours a day." This indicates that the person in question typically works for six hours each day.