You may modify the update delay, it's the 60 (60 seconds) in this line (chose a multiple of 60, like 180 (=3mins)):
.timer.awaywithtime 0 60 away $(%awaywithtime.msg,0) - duration: $!awaywithtime.duration
In the screenshot above you're on MindForge, which should allow more than one away reason per minute.
To hide the additional/repetitive display of your away status in your status window: if you only get the default message "You have been marked as being away" add this line to the script:
raw 306:*: if (%awaywithtime.msg) { haltdef }
If it's another message you see (for example part of your theme), you have to find and modify the respecitve "raw 306" line in your script.