First go to apps.twitter.com and create a new application. Go to Permissions tab and make you that you have read and write access for your application. Then request the access tokens in the Key and Access Tokens tab.
See my previous post about the basic setup.
mypost = 'This is my new tweet' api.update_status(status=mypost)
for follower in tweepy.Cursor(api.followers).items(): follower.follow()
Check cron help at arch linux.
0 */3 * * * /usr/bin/python /path/to/mybot.py