Section 18. The colonel may, in the event of any public emergency, or of any unusual demand for the services of members of the state police serving in any bureau of the department, or whenever he deems it in the public interest, require such members to work additional hours of duty and prevent such members from taking time off when entitled thereto, or at the time assigned therefor; provided, however, that such members shall be compensated for any additional work in accordance with the provision of section thirty C of chapter one hundred and forty-nine.

The colonel may grant further time off to such members, in every instance without loss of compensation.