Time is an important and confusing topic in Splunk. If you want to skip this section, absorb one concept—time must be parsed properly on the way into the index as it cannot be changed later without indexing the raw data again.
If given the date
11-03-04, how would you interpret this date? Your answer probably depends on where you live. In the United States, you would probably read this as November 3, 2004. In Europe, you would probably read this as March 11, 2004. It would also be reasonable to read this as March 4, 2011.
Luckily, most dates are not this ambiguous, and Splunk makes a good effort to find and extract them, but it is absolutely worth the trouble to give Splunk a little help by configuring the time ...