C# correct method to compare 2 date time

Compare datetime as you would compare numbers such as

DateTime expiration_date = newVer.License.Status.Expiration_Date;
DateTime currentDateTime = DateTime.Now;
if( expiration_date < currentDateTime)
{
   // expired 
}

If you need only date and not time then use

  DateTime expiration_date = newVer.License.Status.Expiration_Date.Date;
  DateTime currentDateTime = DateTime.Now.Date;

You can also use day difference of two date.

int daydiff = (int)((currentDateTime - expiration_date).TotalDays)

Your question has a two-part answer. There may be something easier, but:

First, convert your string to a DateTime object. The DateTime class has several methods to help with this. Try ParseExact.

Then, convert the DateTime object to a Unix timestamp.

Now, you have two long ints, that you can compare, and convert the int comparison to another DateTime, and take things from there.