Is there any way through which i can schedule my apex job at the desired time recurring daily. I also want this job to recur after every 15 minutes sometimes. I went through some links including http://help.salesforce.com/apex/HTViewHelpDoc?id=code_schedule_batch_apex.htm and Scheduling an Apex Job through the ui however i can only find that we can schedule our job on a weekly or monthly basis, and that too at the time specified which we cannot modify. Please suggest of any way out so that i can schedule my job daily or recurring after every certain time in a day at a time which i can mention. Thanks in advance.
Exactly as you say, go through the UI, schedule weekly... and then tick the box beside each of the seven days of the week.
You can specify the start time in the drop down at the bottom, although only to the nearest hour.
If you wanted to run the same job 4 times a day then you could achieve this through the UI by setting up four scheduled jobs for your class, one job for each desired start time. Note that you can only have 100 scheduled jobs in total.
For more specific requirements around timing and recurrence you can schedule it through code, there is some more information here, an example would look like this
proschedule p = new proschedule(); String sch = '0 0 8 13 2 ?'; system.schedule('One Time Pro', sch, p);
You would typically run this setup step as anonymous apex, through the developer console.
Cron expressions are really powerful and let you specify different recurrences, precise start times etc.
However remember that the start time you are specifying is the time you would like the job to start, and this is subject to resource availability on the platform.