Problem in reportSettings.php Code

[GitHub-Mike]

http://localhost/organic-search-analytics/report.php

Notice: A non well formed numeric value encountered in C:\xampp71\htdocs\organic-search-analytics\inc\html\reportSettings.php on line 48

Line 46: $diff = strtotime( $row["max"] ) - strtotime( $row["min"] ); // OK!

Line 48: $row["max"] - $row["min"]; // Why? //$row["max"] - $row["min"]; Works!