best way to convert UTC to local time?

["TJ Luoma" <luomat@xxxxxxxxx>]

I am trying to write a script which will sort files into sub-folders 
based on the date that the file was _added_ to the current folder it is 
in.

This is what I have come up with:

	zmodload zsh/datetime

	for F in "$@"
	do

			# if the input IS NOT a file (i.e. is a link or directory), skip it
		[[ -f "$F" ]] || continue

			# see if the input from the user is readable, if not, go on to the 
next one
		[[ -r "$F" ]] || continue

			# look for Spotlight metadata for "Date Added" (kMDItemDateAdded)
			# This will be something like "2013-06-08 02:46:38 +0000"
		DATE_ADDED_UTC=$(mdls -raw -name kMDItemDateAdded "$F")

			# if we get '(null)' then the metadata doesn't exist. Which shouldn't 
happen. But might.
		[[ "$DATE_ADDED_UTC" == "(null)" ]] && continue

			# If we get here, we have the date added, but that date is based on 
UTC time,
			# not local time (currently EDT), so we need to convert it.
			
			# convert that timestamp to seconds-since-epoch
			# this will give us something like '1370677598'
		DATE_ADDED_UTC_EPOCH=$(TZ=UTC strftime -r "%Y-%m-%d %H:%M:%S +0000" 
"$DATE_ADDED_UTC")

			# convert that 'seconds-since-epoch' to a local time
			# 2013-06-08
		DATE_ADDED_LOCAL=$(strftime "%Y-%m-%d" "$DATE_ADDED_UTC_EPOCH")

		echo "The file $F was added on $DATE_ADDED_LOCAL"

	done

This works, but three separate `strftime` calls seems inefficient. I 
mean, it's not like it takes a long time to run or anything, I'm just 
wondering if there's a "better" way.

TjL

p.s. - as far as I know there's no other way to get the "Date Added" 
info. If I'm wrong, please let me know :-)