gnome-shell-timer-config: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/gnome-shell-timer-config - from package: gnome-shell-timer

You may install the required package with command apt-get install {package}

Error in other languages:
gnome-shell-timer-config: bevel nie gevind nie
gnome-shell-timer-config: comandă negăsită
gnome-shell-timer-config: comando não encontrado
gnome-shell-timer-config: commande introuvable
gnome-shell-timer-config: command not found
gnome-shell-timer-config: käsku ei ole
gnome-shell-timer-config: không tìm thấy lệnh
gnome-shell-timer-config: komanda nerasta
gnome-shell-timer-config: Kommando nicht gefunden.
gnome-shell-timer-config: kommandot finns inte
gnome-shell-timer-config: komut yok
gnome-shell-timer-config: nie znaleziono polecenia
gnome-shell-timer-config: níor aimsíodh an t-ordú
gnome-shell-timer-config: no se encontró la orden
gnome-shell-timer-config: no s'ha trobat l'ordre
gnome-shell-timer-config: opdracht niet gevonden
gnome-shell-timer-config: parancs nem található
gnome-shell-timer-config: perintah tidak ditemukan
gnome-shell-timer-config: príkaz nenájdený
gnome-shell-timer-config: příkaz nenalezen
gnome-shell-timer-config: команда не найдена
gnome-shell-timer-config: командата не е открита
gnome-shell-timer-config: 命令找不到
gnome-shell-timer-config: コマンドが見つかりません