29 CFR § 570.35
Hours standards. Except as provided in paragraph (c) of this section, employment in any of the permissible occupations to which this subpart is applicable shall be confined to the following periods:
(1) Outside of school hours;
(2) Not more than 40 hours in any 1 week when school is not in session;
(3) Not more than 18 hours in any 1 week when school is in session;
(4) Not more than 8 hours in any 1 day when school is not in session;
(5) Not more than 3 hours in any 1 day when school is in session, including Fridays;
(6) Between 7 a.m. and 7 p.m. in any 1 day, except during the summer (June 1 through Labor Day) when the evening hour will be 9 p.m.