I think that the proper equivalent would be 35h/week for full time remote position. Like you said you can't possibly expect an employee in an office to do actual, raw 8h of work between 9 to 5. And when you do your remote work schedule, you can't expect yourself to work 8h without a break and be productive so requiring 40h is like 45h when translated to an on site job. I know there's no transit cost but it should not be an excuse to require more hours from remote workers.