Convert groov Trend timestamp in Excel

Can somebody please tell me how this timestamp works? I’ve search up and down, when I download a trend, this is what the timestamp looks like

1610696540336 this is what this should represent Friday Jan 15 07:42:20
how can i make this use able?

Here is a handy site for quick conversion.

If you search this forum for ‘epoch’ there are a few posts .
Here is one: Save groov trend data to a CSV file on the AR1

And Optos very own ‘Convert Date Stamps’ from the drop down menu on our website;
https://opto22.com/support/resources-tools/demos/convert-date-stamps-(groov-to-excel)

If you got the data in excel, you can use this formula: =A1/86400000+(-7/24)+DATE(1970,1,1) where A1 is the cell the date is in and the -7 in the (-7/24) is the timezone offset in hours. You may need to tell Excel to format as date and time.

Thanks, philip this works good
=A2/86400000+(0/24)+DATE(1970,1,1)