Você pode tentar o comando abaixo do awk one-liner,
awk 'NF{ $1=strftime("%c", $1);}1' file
OR
$ awk 'NF>1{ $1=strftime("%c", $1);}1' file
Monday 22 September 2014 06:54:14 AM IST 08:11:96:e9:52:ec 192.168.1.96 W11837894 *
Tuesday 23 September 2014 12:48:48 AM IST b4:b6:76:0c:c9:4d 192.168.1.46 root-HP-9470m *
Sunday 21 September 2014 07:00:16 AM IST 00:1b:21:0e:f2:bd 192.168.1.219 root-Dell-DM061 *
Monday 22 September 2014 09:10:37 AM IST 00:01:2e:4d:49:bd 192.168.1.31 ata *
Sunday 21 September 2014 07:00:41 AM IST 00:30:67:d2:25:65 192.168.1.51 root-TA75M *