Sample Code:
YourScheduledApexClass obj = new YourScheduledApexClass(); String sch1 = '0 0 * * * ?'; System.schedule('Schedule Job1', sch1, obj); String sch2 = '0 15 * * * ?'; System.schedule('Schedule Job2', sch2, obj); String sch3 = '0 30 * * * ?'; System.schedule('Schedule Job3', sch3, obj); String sch4 = '0 45 * * * ?'; System.schedule('Schedule Job4', sch4, obj);