Advice on what to say when quitting

I've worked at my current role for about a year and a quarter.

The hours have started to hit really hard. I'm consistently working over 60 hours a week.

I was also told that I was disappointing my mentor with my work. Given the amount of work, I simply feel that it is a futile effort to improve this relationship.

All and all, I think it's time for a change.

When I am applying for other roles, what is the best way to verbalize this in my interviews without sounding lazy and/or stupid.

Any advice?

TL;DR: I'm about to switch roles. When interviewing, what is the best way to verbalize that I would like to work a 40 hour work week?

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