If you hold a stock for >45 days, the franking credits are yours...

If you hold a stock for >45 days, the franking credits are yours to claim. And you need to have >30% economic interest in the holding (i.e. not hedge your position with derivatives to the value of >30%).

If you're claiming less than $5000 in franking credits, then you can claim them even if you hold a stock for less than 45 days.

http://www.ato.gov.au/businesses/content.asp?doc=/content/18898.htm&pc=001/009/025/002/001&mnu=&mfp=&st=&cy=1

Anyway, why plan to sell in a month when you can get your fair share of market returns by hanging onto them forever?