Time Event
11/19/10 11:59:37.000 PM Nov 18 23:59:37 10.0.0.10 Nov 19 04:59:37 filterlog: 81,16777216,,1446589294,fxp0,match,pass,in,4,0x0,,1,9886,0,none,2,igmp,28,10.0.0.13,224.0.0.251,datalength=8
date_second = 37
host = 10.0.0.10
index = main
source = udp:5140
sourcetype = PFsense1
i'm guessing that splunk can't parse the PFsense timestamp. You may need to update/modify the sourcetype def.