Parsing large xlsx file, Date format case

Question

Because xlsx file may contain million rows, I decided to use poi event model, took example from here(ExampleEventUserModel), but found some problem parsing Date format cells.

For example I have in excel date 01.10.2011 in cell A15, but xml has:

<c r="A15" s="11"><v>40817</v></c>

It is not in date format, even not in millis for example.

How to parse date for event model?

Best regards.