It's been a while since my last visit, but it's good to be back

I have a question about xslt:
I have an xml document and I need to transform it to another xml document.
One has a date formatted as: yyyy/mm/dd hh:mm:ss
the other document should have the date 3 times in it:
- once as a timestamp: miliseconds since 1970 yada yada yada
- once in the format: yyyy-mm-dd hh:mm
- once in the format: dd/mm/yyyy

The last two shouldn't be a problem.
But the timestamp is giving me headaches

How can I transform a textual date to a timestamp using xslt (is it even possible)?

Kind regards.