AppleScript:
tell application "Safari"
set theDocument to make new document at end of documents
set theWindow to window 1
tell theWindow
repeat
set properties of tab 1 to {URL:"http://www.apple.com"}
delay 60
set properties of tab 1 to {URL:"http://www.google.com"}
delay 60
end repeat
end tell
end tell
This alternates between URLs just to prove that it works.
Delay value is in seconds. So this example does 1 minute between reloads.
The important part is to grab a reference to the newly created window once it is created. Now you can refer to it even if new windows are created on top of this one.
The repeat loop here will repeat forever.
-numero