Update spec/registry.md

Author: eemeli

spec/registry.md

@@ -907,7 +907,7 @@ are encouraged to track development of these options during Tech Preview:
 
 When an _operand_ or an _option_ value uses a _variable_ annotated,
 directly or indirectly, by a `:datetime` _annotation_,
-its resolved value contains the implementation-defined datetime value
+its resolved value contains an implementation-defined date/time value
 of the _operand_ of the annotated _expression_,
 together with the resolved options values.