how to grep and compare timestamp in a file with the current date

UNIX AIX
1

I want to read a log file from a particular location.In the log file each line starts with timestamp.I need to compare the timestamp in the logfile with the current date.If the timpestamp in the log file is less than 4 hours then i need to read the file from that location.Below is the file format.Please help as its urgent.
[4/30/09 4:03:51:100 EST] 00000070 AdminServiceI W ADMN0037W:
[4/30/09 4:04:12:064 EST] 00000721 InvalidateByI E DYNA0052E:
[4/30/09 4:04:47:335 EST] 000000e1 LeaseAlarm I SCHD0134I:
[4/30/09 4:05:21:015 EST] 00000070 AdminServiceI W ADMN0037W:
[4/30/09 4:06:51:079 EST] 00000070 AdminServiceI W ADMN0037W:

2

what have you tried till now??
HINT:convert the time stamps in min then subtract and convert them back to hours
try to impliment this logic..