I don't know that this is much better in practice than your solution of just running sleep once, but you could run your check with a while loop instead of an if statement:
#!/bin/sh while ! pgrep -f "notification-daemon" > /dev/null; do /usr/lib/notification-daemon/notification-daemon & sleep 0.1 done notify-send "Take 5" aplay /home/Me/Music/brubek-clip.wav This should guarantee that you don't continue until the daemon is running (e.g. if for some reason it takes longer than your 0.5 second sleep).