Nice and concice. If the poster meant "in the last 24 hours" to mean this calendar day, let's combine this concise answer with some of the others above:

   
    if ( 1 > -M $file and 
          (localtime((stat _)[9]))[3] == (localtime)[3] ) {
               # modified "in the last 24 hours"
        }
[download]

Beware of small, subtle bugs around Daylight Savings time.