Day/Month/Year doesn't display without hours

Specify a format string when performing the conversion. Don't Convert.ToString, which doesn't allow for different format strings - call ToString on the DateTime. For example:

DateTime updated = context.SP_GetDate().FirstOrDefault().UpdateTime;
string updatedText = updated.ToString("d");

Here, d is the "short date" standard date/time format specifier. There are others to choose from.

Alternatively, you could specify a custom date/time format, e.g.

DateTime updated = context.SP_GetDate().FirstOrDefault().UpdateTime;
string updatedText = updated.ToString("yyyy-MM-dd"); 

Note that these will use the "current culture" for localization, picking the language, standard date format, month names etc. You can specify a different culture if you need to - typically the invariant culture, used for machine to machine communication:

DateTime updated = context.SP_GetDate().FirstOrDefault().UpdateTime;
string updatedText = updated.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture);