Clarify time units usage in docs

This commit clarifies the distinction between supported time units for
durations and supported time units for durations in the docs.

Relates #19159

docs/reference/aggregations/bucket/datehistogram-aggregation.asciidoc

@@ -26,8 +26,9 @@ Requesting bucket intervals of a month.
 
 Available expressions for interval: `year`, `quarter`, `month`, `week`, `day`, `hour`, `minute`, `second`
 
-
-Fractional values are allowed for seconds, minutes, hours, days and weeks. For example 1.5 hours:
+Time values can also be specified via abbreviations supported by <<time-units,time units>> parsing.
+Note that fractional time values are not supported, but you can address this by shifting to another
+time unit (e.g., `1.5h` could instead be specified as `90m`).
 
 [source,js]
 --------------------------------------------------
@@ -36,15 +37,13 @@ Fractional values are allowed for seconds, minutes, hours, days and weeks. For e
         "articles_over_time" : {
             "date_histogram" : {
                 "field" : "date",
-                "interval" : "1.5h"
+                "interval" : "90m"
             }
         }
     }
 }
 --------------------------------------------------
 
-See <<time-units>> for accepted abbreviations.
-
 ==== Keys
 
 Internally, a date is represented as a 64 bit number representing a timestamp

docs/reference/aggregations/bucket/diversified-sampler-aggregation.asciidoc

@@ -153,5 +153,7 @@ In this situation an error will be thrown.
 The de-duplication logic in the diversify settings applies only at a shard level so will not apply across shards.
 
 ===== No specialized syntax for geo/date fields
-Currently the syntax for defining the diversifying values is defined by a choice of `field` or `script` - there is no added syntactical sugar for expressing geo or date units such as "1w" (1 week).
-This support may be added in a later release and users will currently have to create these sorts of values using a script.
+Currently the syntax for defining the diversifying values is defined by a choice of `field` or
+`script` - there is no added syntactical sugar for expressing geo or date units such as "7d" (7
+days). This support may be added in a later release and users will currently have to create these
+sorts of values using a script.

docs/reference/api-conventions.asciidoc

@@ -171,8 +171,18 @@ one or more maths expressions:
 * `-1d` - subtract one day
 * `/d`  - round down to the nearest day
 
-The supported <<time-units,time units>> are: `y` (year), `M` (month), `w` (week),
-`d` (day), `h` (hour), `m` (minute), and `s` (second).
+The supported time units differ than those supported by <<time-units, time units>> for durations.
+The supported units are:
+
+[horizontal]
+`y`:: years
+`M`:: months
+`w`:: weeks
+`d`:: days
+`h`:: hours
+`H`:: hours
+`m`:: minutes
+`s`:: seconds
 
 Some examples are:
 
@@ -348,21 +358,17 @@ of supporting the native JSON number types.
 [float]
 === Time units
 
-Whenever durations need to be specified, eg for a `timeout` parameter, the
-duration must specify the unit, like `2d` for 2 days.  The supported units
-are:
+Whenever durations need to be specified, e.g. for a `timeout` parameter, the duration must specify
+the unit, like `2d` for 2 days.  The supported units are:
 
 [horizontal]
-`y`::   Year
-`M`::   Month
-`w`::   Week
-`d`::   Day
-`h`::   Hour
-`m`::   Minute
-`s`::   Second
-`ms`::  Milli-second
-`micros`::  Micro-second
-`nanos`::  Nano-second
+`d`::       days
+`h`::       hours
+`m`::       minutes
+`s`::       seconds
+`ms`::      milliseconds
+`micros`::  microseconds
+`nanos`::   nanoseconds
 
 [[byte-units]]
 [float]

docs/reference/migration/migrate_5_0/aggregations.asciidoc

@@ -26,3 +26,8 @@ for `from` and `to` anymore.
 `size: 0` is no longer valid for the terms, significant terms and geohash grid
 aggregations. Instead a size should be explicitly specified with a number greater
 than zero.
+
+==== Fractional time values
+
+Fractional time values (e.g., 0.5s) are no longer supported. For example, this means when setting
+date histogram intervals "1.5h" will be rejected and should instead be input as "90m".

docs/reference/migration/migrate_5_0/settings.asciidoc

@@ -291,6 +291,5 @@ still defaults to `true` in that case.
 
 The unit 'w' representing weeks is no longer supported.
 
-Fractional time values (e.g., 0.5s) are no longer supported. For
-example, this means when setting timeouts "0.5s" will be rejected and
-should instead be input as "500ms".
+Fractional time values (e.g., 0.5s) are no longer supported. For example, this means when setting
+timeouts "0.5s" will be rejected and should instead be input as "500ms".