Timer in bash script not accurate when using it with longer times

Question

#!/bin/bash

# get user input
ZENITY1=$(zenity --entry --text '  1m:    60s\n  5m:   300s\n10m:   600s\n15m:   900s\n20m: 1200s\n25m: 1500s\n30m: 1800s\n35m: 2100s\n40m: 2400s\n45m: 2700s\n50m: 3000s\n55m: 3300s\n   1h: 3600s' --entry-text "Input only int in seconds!" --title "Timer")

# put starting date in variable
STARTTIME=$(date)

# audit/check user input
WAITINGTIME=$(echo $ZENITY1 | egrep "[0-9]{1,}" -o)
if [ "$WAITINGTIME" == "" ]; then exit 1; fi

# main stopwatch
for i in `seq $WAITINGTIME -1 1`; do echo $i | osd_cat -A left -p top -i 100 -c black -d 1; done

# time expired message
zenity --info --text="Time expired@\n$(date)\n\nStarted@\n$STARTTIME"

So this is the script that I have on my desktop. If I need to warn somebody for e.x.: "please warn me after 15 minutes". But if I use it in a longer time, e.x.: 12 hours it's not very accurate! it could get ~10 minutes difference to the real time... :\ Why is it?

Answer 1

If you find it takes consistently too long, I guess you're seeing the overhead of fourty-odd thousand executions of echo and osd_cat.