batch offset timestamps in photos

offsettimestamp.sh

#!/bin/bash
for f in DP2Q*.*; do
    ts="$(GetFileInfo -d "$f")"
    e="$(date -j -f "%m/%d/%Y %H:%M:%S" "$ts" +%s)"
    ((o=60*60*24*60-27120))
    ((e+=o))
    nd="$(date -r $e "+%m/%d/%Y %H:%M:%S")"
    SetFile -m "$nd" "$f"
    SetFile -d "$nd" "$f"
done