Continually check for file

I need a script or bat that will open a saved session and put a trigger file (trigger.txt) to the FTP server then continually or loop to check for a generated file (trigger.blt) for up to 5 minutes or I suppose until the file is present then pull or get a different file (downlaod.txt)
I've tried various if not errorlevel checks etc but can't seem to figure out.
Any help is much appreciated!

Please start here: Checking file existence.

If you need further help, please post what you have tried.