The data structure depends on what you want to do with that data, not what the data looks like.

Since you want to sort it chronologically I assume the most frequent operation will be to look for all items between two dates. In that case a simple array would be best (i.e. the solution you would use as shell programmer too).

Sorting is done with the sort() function. You can provide sort() with a function it uses to compare two items (aliasing the items to $a and $b). In your case something like this would work:

my @sorted= sort { $b<=>$a } @unsorted;
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You can read the perl documentation of the sort function for more info (with perldoc -f sort)

Generally a hash is not suitable for storing sorted data.