Keystone First Hours: Mon. - Fri., 8 a.m. - 5 p.m. Nurse on call 24 hours a day 1-800-521-6007: Mental Health/Substance Abuse Magellan Healthcare, Inc. Customer Service and Precertification 24 hours a day, 7 days a week: 1-800-688-1911: For Keystone Health Plan East Members with Caring Foundation benefits 24 hours a day, 7 days a week: 1 ....