how to start workflow automatically daily at a perticular time

Use the K2 API and create a console app to start the desired process.  Then schedule the console app to run using Windows Task Scheduler.

Example here.

You may want to try this if you're using SharePoint 2010 or if using 2013 but have installed the K2 for SharePoint 2010 components:

http://help.k2.com/helppages/k2blackpearlUserGuide4.6.4/Process_Portal_-_Process_Management_-_Scheduler.html

Hi

https://help.k2.com/onlinehelp/k2blackpearl/userguide/4.6.4/webframe.html#process_portal_-_process_management_-_scheduler.html

How to do this programmatically?

Regards,

Asad Naeem

I think an API will be great.

However I post a while back a Post that explain how to use the Windows Scheduler and securely schedule Loops and Workflows in BlackPearl for reminders and notifications.

http://community.k2.com/t5/K2-blackpearl/Ability-to-schedule-Loops-and-Workflows-in-BlackPearl/m-p/86451#M26656

Hope this helps =)