salesforce - Schedule a batch at certain hours -

i made schedulable batch want run @ hours, let's 6, 12 , 18. i'm writting hours in custom setting cs_schedule__c. how can call cs apex , hours?

thanks in advance.

here page outlining how retrieve custom settings in apex depending on if it's list or hierarchy custom settings.

as far scheduling, can in apex if wish, so:

classtoschedule schcls = new classtoschedule(); string sch = '20 30 8 10 2 ?'; string jobid = system.schedule('name of job', sch, schcls); 

the sch string cron expression represent time runs. check out cron expression builder more info. instead of using numbers build string data in custom setting.