I just made the following script for this purpose. I named it timelimit:

#!/bin/bash



#timelimit - Set daily time limits for specific applications



#Licensed under the standard MIT license:

#Copyright 2013 Radu Rădeanu (https://askubuntu.com/users/147044/).

#Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

#The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

#THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE



if [ $# -ne 1 ];then

    echo "Usage: `basename $0` APP_NAME"

    exit 1

fi



export DISPLAY=:0



app_name=$@

time_to_play_daily="2:30:00"  # channge as you wish; the format is: H[:M[:S]]

file="$HOME/.count_time_$app_name"



if [ -a $file ]; then

    if [ "$(head -1 $file)" != "$(date +%D)" ]; then

        echo $(date +%D) > $file

        echo $time_to_play_daily >> $file

    fi

else 

    touch $file

    echo $(date +%D) >> $file

    echo $time_to_play_daily >> $file

fi



time_to_play_left=$(sed -n '2p' $file)



sec_left=$(echo $time_to_play_left | awk -F: '{ print ($1 * 3600) + ($2 * 60) + $3 }')



function countdown

{

    sec_left=$(echo $time_to_play_left | awk -F: '{ print ($1 * 3600) + ($2 * 60) + $3 }')

    local start=$(date +%s)

    local end=$((start + sec_left))

    local cur=$start



    while [[ $cur -lt $end ]]; do

        pid=$(pgrep -x $app_name)

        if [ "$pid" != "" ]; then

            cur=$(date +%s)

            sec_left=$((end-cur))

            time_to_play_left="$((sec_left/3600)):$(((sec_left/60)%60)):$((sec_left%60))"

            sed -i "2s/.*/$time_to_play_left/" $file

            # next line is useful only when you test from terminal

            printf "

Time left to play with %s: %02d:%02d:%02d" $app_name $((sec_left/3600)) $(((sec_left/60)%60)) $((sec_left%60))

            sleep 1

        else

            break

        fi

    done

}



while : ; do

    pid=$(pgrep -x $app_name)

    sleep 1

    if [ "$pid" != "" ]; then

        if [ $sec_left -gt 0 ]; then

            notify-send -i $app_name "Time left to play with $app_name for today: $time_to_play_left"

        else

            notify-send -i "error" "Your time to play with $app_name has finished for today!"

        fi

        countdown $time_to_play_left

        pid=$(pgrep -x $app_name)

        if [ "$pid" != "" ]; then kill $pid; fi

    fi

done

Don't forget to make it executable:

chmod +x timelimit

Syntax:

timelimit APP_NAME

Important:

• You can test this script in terminal, but it should be to run at system startup. To make it to run at startup, see How to run scripts on start up?



• This script should be restarted at midnight if you don't turn off your computer at night. To do this you can add a cron job like:

  
  
  

  
  
  00 00 * * * kill `pgrep -x timelimit` && timelimit APP_NAME
  
  

  
  
  

  More about: https://help.ubuntu.com/community/CronHowto