[Docs] Add date math examples to api-conventions.asciidoc (#25217)

Author: markwalkom

docs/reference/api-conventions.asciidoc

@@ -215,13 +215,12 @@ The supported units are:
 `m`:: minutes
 `s`:: seconds
 
-Some examples are:
+Assuming `now` is `2001-01-01 12:00:00`, some examples are:
 
-[horizontal]
-`now+1h`::              The current time plus one hour, with ms resolution.
-`now+1h+1m`::           The current time plus one hour plus one minute, with ms resolution.
-`now+1h/d`::            The current time plus one hour, rounded down to the nearest day.
-`2015-01-01||+1M/d`::   `2015-01-01` plus one month, rounded down to the nearest day.
+`now+1h`:: `now` in milliseconds plus one hour. Resolves to: `2001-01-01 13:00:00`
+`now-1h`:: `now` in milliseconds plus one hour. Resolves to: `2001-01-01 11:00:00`
+`now-1h/d`:: `now` in milliseconds rounded down to UTC 00:00. Resolves to: `2001-01-01 00:00:00``
+ `2001-01-01\|\|+1M/d`:: `now` in milliseconds plus one month. Resolves to: `2001-02-01 00:00:00`
 
 [float]
 [[common-options-response-filtering]]