If the input string is always "MM:DD:YYYY,HH:MI:SS,FLOAT", the the minutes field ("MI") is always the fourth colon-delimited substring (regardless of the number of digits in each field). So this is all you need:
my $string = "01:01:2000,14:01:12,1.584167";
my $minute = (split( /:/, $string ))[3];