Get last file modification date of application data files?

I have a plist file in my application data that i want to update from a webserver every 24 hours. Is there a way to check when the file is last modified or should i, in some way register the date and time when i update the file, and use that to compare to?

if (lastMod > currentDate){
    [arrayFromXml writeToFile:path atomically:YES];
}