Zenity and bulk file movements

Hi all.

Total beginner to Zenity.
I've plagiarised bits of code from all over to try to get something to work.

The story:
I have a directory with maybe 10-15 files in it, each about 200MB.
i send these files one at a time to a drive about 15 miles away. The Synology sync can only handle one file at a time, as because there is no high speed line, the file takes about an hour to send. More than 1 file at a time, and Synology can't handle it.
I send at night using the script below.

#!/bin/bash
(
cd ~/Downloads
d1="$(zenity  --file-selection --title="Bulk Move    Choose starting directory"  --directory)"
d2="$(zenity  --file-selection --title="Bulk Move    Choose destination directory"  --directory)"
delay="$(zenity --entry --title="Bulk Move" --text="Enter delay in minutes:")"
result=`echo "$delay *60" | bc`
find "$d1"/* -exec mv {} "$d2" \; -exec sleep "$result" \;

) | zenity --title="Timed Bulk Move in progress" --progress --pulsate --auto-close &

# get zenity process id
PID_ZENITY=${!}

# get firstly created child process id, which is running all tasks
PID_CHILD=$(pgrep -o -P $$)

# loop to check that progress dialog has not been cancelled
while [ "$PID_ZENITY" != "" ]
do
  # get PID of all running tasks
  PID_TASKS=$(pgrep -d ' ' -P ${PID_CHILD})

  # check if zenity PID is still there (dialog box still open)
  PID_ZENITY=$(ps h -o pid --pid ${PID_ZENITY} | xargs)

  # sleep for 2 second
  sleep 2
done

# if some running tasks are still there, kill them
[ "${PID_TASKS}" != "" ] && kill -9 ${PID_TASKS}
zenity --info --text "Move Completed"

I have not put things in the right place, as when the last file is gone, it counts another delay until it completes.

I would dearly love the progress bar to count up as the delay completes, but have not got a clue. Sitting looking at a Cylon for 45 minutes ain't doing me any good.