I suggest to use this third party plugin:
(download on the top left link on the page)
Then you go like:
On Start of Layout
Set [Global Text Variable] to (Date.Year & "/" & Date.Date & "/" & Date.Day & "/" & Date.Hours & "/" &Date.Minutes)
Then you need to put this into the localstorage / webstorage and restore the date upon a new game session from there and compare.
It's pretty tricky to do for a beginner, I suppose, but this way, it will work.
Edit: Or maybe you want to store year, date, day, hours and minutes into different variables for easier handling. I believe that may be easier.
Edit: The plugin appearently also supports Date.Date2UnixTimestamp.