Well I'll need some more clarification, what is your intention with refreshing the page? It is possible to make the page change location (which could be to itself), however without something else on the page this is kind of pointless.
if( data == "Database Backup in T-Minus 0 minutes 0 seconds!" )
Obviously there's ways to spruce this up in PHP. Such as making it display "Starting Backup!" when the minutes and seconds variables hit 0. Your coding level should allow you to do this without my assistance.