If you want to trigger an event when you go away, you could include a seperate alias within your away statment, like
set %away.seconds 0
/custom-alias <~~~~ make this be your event, or trigger your event
/another-alias <~~~ do something else with this...
.timer.away 0 1 away-alias (or command) <~~ set a timer for another alias or command, whatever you want.
set %away.total $replace($duration(%away.seconds),hrs,hs,hr,h,mins,m,min,m,secs,s,sec,s)
As far as keeping track of your time, you could set a variable to the time you went away, and then set a timer to keep track of the seconds (or minutes) away.... increment it one second at a time, and then use this on return:
/msg $chan Im now back after %away.total
I use this for mine. It doesnt have days or weeks in it, because if im away that long, i type /quit
You sound like your away time isnt your goal, but maybe you could use this type of example to keep track of your active time as well... set a variable to your time away, then subtract the difference?... im not sure what youre exact goal is, but maybe this would help.