C# - SQL Group By Column Value In LINQ?

I am trying to translate this:

SELECT IDNum, Max(Convert(varchar(20), (TimeOut - TimeIn), 108))
FROM IO_Times Group by IDNum
order by Max(Convert(varchar(20), (TimeOut - TimeIn), 108)) desc";

Into LINQ in C#. The above returns a list of the maximum value of (TimeOut-TimeIn) that corresponds to each unique IDNum (There are multiple TimeOut-TimeIn values for every IDNum).Here is what I am trying now:

from IO_Time in db.IO_Times
orderby SqlMethods.DateDiffMinute(IO_Time.TimeIn, IO_Time.TimeOut) descending
group IO_Time by IO_Time.IDNum into list
select new
{
ID = list.Key,
Time = list
});

This returns the correct IDs in the correct order, but the "list" contains everything in the database entry (which makes sense). I have also tried group by IDNum and Time, but then I get unique time entries and multiple IDs returned.I could do a foreach loop and manually sort it all out, but I would really rather not do that.