After testing Jerry solution, I found a problem. If your AppleScript App is not "topped" at the time of the event, you may get an AppleScript error and the only think that will call you is the blinking of the icone in the doc.
So I've made a small change:
Open the AppleScript editor and type this:
on idle
tell application "call_me"
activate
end tell
display dialog "Back to work" buttons "Work!" default button "Work!"
return 3600
end idle
Save the script while selecting "Aplication" in the bottom menu of the file selector and then checking "Don't quit" (in French "Ne pas quitter aprés l'exécution") so the App will stay active even after the event.
You must give the name "call_me" to your app or, if you change the name, change also this name in the code (tell application "xxxx" activate)
Each 3600 seconds, the App will be topped and then will display the alert box.
Just one point: the first time you'll save the App, Applescript will show you a selector, and ask you "Where is call_me.app?" Just cancel this selector and save.
Oh!! I've to go back to work!!
