chore: add note about chunks. (#4420)

* chore: add note about chunks.

* chore: update on review.

* Update api/hypertable/set_chunk_time_interval.md

Co-authored-by: Erik Nordström <819732+erimatnor@users.noreply.github.com>
Signed-off-by: Iain Cox <iain@timescale.com>

* chore: update on review.

---------

Signed-off-by: Iain Cox <iain@timescale.com>
Co-authored-by: billy-the-fish <iain@tigerdata.com>
Co-authored-by: Erik Nordström <819732+erimatnor@users.noreply.github.com>

Author: billy-the-fish

api/hypertable/set_chunk_time_interval.md

@@ -32,12 +32,22 @@ UNIX epoch, set `chunk_time_interval` to 24 hours:
 SELECT set_chunk_time_interval('conditions', 86400000);
 ```
 
-## Required arguments
+## Arguments
 
-|Name|Type|Description|
-|-|-|-|
-|`hypertable`|REGCLASS|Hypertable or continuous aggregate to update interval for|
-|`chunk_time_interval`|See note|Event time that each new chunk covers|
+
+| Name        | Type             | Default | Required                                                             | Description                                                                                                                                      |
+|-------------|------------------|---------|----------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------|
+|`hypertable`|REGCLASS| -       | ✔                                                                    | Hypertable or continuous aggregate to update interval for.                                                                                       |
+|`chunk_time_interval`|See note|-       | ✔   | Event time that each new chunk covers.                                                                                                           |
+|`dimension_name`|REGCLASS|-       | ✖ | The name of the time dimension to set the number of partitions for. Only use `dimension_name` when your hypertable has multiple time dimensions. |
+
+If you change chunk time interval you may see a chunk that is smaller than the new interval. For example, if you 
+have two 7-day chunks that cover 14 days, then change `chunk_time_interval` to 3 days, you may end up with a 
+transition chunk covering one day. This happens because the start and end of the new chunk is calculated based on 
+dividing the timeline by the `chunk_time_interval` starting at epoch 0. This leads to the following chunks 
+[0, 3), [3, 6), [6, 9), [9, 12), [12, 15), [15, 18) and so on. The two 7-day chunks covered data up to day 14: 
+[0, 7), [8, 14), so the 3-day chunk for [12, 15) is reduced to a one day chunk. The following chunk [15, 18) is 
+created as a full 3 day chunk.
 
 The valid types for the `chunk_time_interval` depend on the type used for the
 hypertable `time` column:
@@ -56,15 +66,5 @@ hypertable `time` column:
 
 For more information, see [hypertable partitioning][hypertable-partitioning].
 
-## Optional arguments
-
-|TEXT|Description|
-|-|-|-|
-|`dimension_name`|REGCLASS|The name of the time dimension to set the number of partitions for|
-
-You need to use `dimension_name` argument only if your hypertable has multiple
-time dimensions.
-
-
 
 [hypertable-partitioning]: /use-timescale/:currentVersion:/hypertables/#hypertable-partitioning