NECHE’s policy on credit hours, based on the US Dept of Education requirements, is as follows:
The Commission defines a credit hour as an amount of work represented in intended learning outcomes and verified by evidence of student achievement that is an institutional established equivalence that reasonably approximates not less than
• (1) One hour of classroom or direct faculty instruction and a minimum of two hours of out of class student work each week for approximately fifteen weeks for one semester or trimester hour of credit, or ten to twelve weeks for one quarter hour of credit, or the equivalent amount of work over a different amount of time; or
• (2) At least an equivalent amount of work as required in paragraph (1) of this definition for other academic activities as established by the institution including laboratory work, internships, practica, studio work, and other academic work leading to the award of credit hours.
You can find the full Policy here: https://www.neche.org/wp-content/uploads/2018/12/Pp111_Policy_On_Credits-And-Degrees.pdf
So for a three-credit course offered over 15 weeks, one should have 3 contact hours per week (note that in practice an hour typically is 50 minutes) and a minimum of 6 hours of out-of-class work by the student. For asynchronous online instruction, some of the 3 weekly faculty class-contact hours may take different forms from what one might expect for an in-seat class. Note that the key driver here is “equivalent work.” It is incumbent upon the University and faculty to show that if the term differs in length from the standard 15 weeks, or the contact class hours differ from 3 hours per week, that whatever arrangement of classes and length of term the institution/faculty member uses an equivalent amount of work and learning outcomes still apply.