For the following entry, should I journalize that entry on the purchased date or on Oct. 1st?

Sept 29, 2009 Purchased a one-year public liability insurance policy for $5,000.
The policy becomes effective at 12:01 a.m. October 1, 2009.

To determine when to journalize the entry for the purchase of the insurance policy, you need to consider the accounting principle called the "matching principle."

The matching principle states that expenses should be recognized in the same accounting period as the revenues they help to generate. In this case, the insurance policy is intended to cover potential liabilities during the year starting from October 1st, 2009.

Therefore, you should journalize the entry on Oct. 1st, 2009, because that is when the insurance policy becomes effective and its coverage aligns with the period for which the premium was paid.