Add naming guidance for date-time values

Author: mikekistler

azure/ConsiderationsForServiceDesign.md

@@ -116,6 +116,8 @@ For example, `collectedItems` not `itemsCollected`
 
 For example, `nextUrl` not `nextURL`.
 
+:ballot_box_with_check: **YOU SHOULD** use "DateTime" suffix in names of `date-time` values.
+
 :ballot_box_with_check: **YOU SHOULD** use a suffix of the unit of measurement for values with a clear unit of measurement (such as bytes, miles, and so on). Use a generally accepted abbreviation for the units (e.g. "Km" rather than "Kilometers") when appropriate.
 
 :ballot_box_with_check: **YOU SHOULD** use an int for time durations and include the time units in the name.