When dealing with time formats:

z gives -5

zz gives -0500

zzz gives -0500 GMT

So, you can format time with -5 using:

//echo -a $time(hh:nntt z) GMT

The output of that line would be:
4:35pm -5 GMT

You can use these same formats for $asctime, $time, and $date. Obviously you don't want to include //echo -a with it when putting it somewhere. That's just to show an example.

And, just so you know, most ISPs aren't going to do much about spam on IRC. Logs can very easily be doctored. Also, many times, spam is caused by a trojan and the person with it doesn't even know they have it or that they are sending out the messages. Chances of you getting RR to do anything is minimal no matter what logs you offer them.