Is it possible to assign different timestamps based on log line contents within the same sourcetype?

I am sending "pan:traffic" logs from our Palo Alto 3050 firewall to Splunk. I want the "_time" fields to be the same value as the "start_time" field when the log line contains "start" and use the time stamp that follows "PA-3050 1," when the log line contains "end" Is it possible to do different time stamps for events in the same source-type "pan:traffic" ? I've bolded the time stamps I want to use for each in the samples below: **Sample start log line:** Feb 14 09:07:25 PA-3050 1,2017/02/14 09:07:25,001701007055,TRAFFIC,start,0,2017/02/14 09:07:25,10.0.0.1,77.000.000.88,0.0.0.0,0.0.0.0,User-to-Ext-Allow-DLP,domain\user,,web-browsing,vsys1,trust,untrust,ethernet1/2,ethernet1/1,LF-LOG-ALLOW,2017/02/14 09:07:25,55537,1,58861,80,0,0,0x0,tcp,allow,740,678,62,4,**2017/02/14 09:07:24**,0,any,0,442739216,0x0,10.0.0.0-10.255.255.255,US,0,3,1,n/a,0,0,0,0,,PA-3050,from-policy **Sample end log line:** Feb 14 10:21:25 PA-3050 1,**2017/02/14 10:21:24**,001701007055,TRAFFIC,end,0,2017/02/14 10:21:24,10.1.1.2,8.8.8.8,0.0.0.0,0.0.0.0,IntDC-to-ExtDNS,,,dns,vsys1,trust,untrust,ethernet1/2,ethernet1/1,LF-LOG-ALLOW,2017/02/14 10:21:24,256848,1,50770,53,0,0,0x19,udp,allow,842,85,757,2,2017/02/14 10:20:52,30,any,0,443053418,0x0,10.0.0.0-10.255.255.255,US,0,1,1,aged-out,0,0,0,0,,PA-3050,from-policy