docs: update the labels timespan info (#6019)

* docs: update the labels timespan info

* updated docs

Co-authored-by: Karen Miller <84039272+KMiller-Grafana@users.noreply.github.com>

* updated docs

Co-authored-by: Karen Miller <84039272+KMiller-Grafana@users.noreply.github.com>

Co-authored-by: Karen Miller <84039272+KMiller-Grafana@users.noreply.github.com>

docs/sources/api/_index.md

@@ -387,8 +387,9 @@ $ curl -G -s  "http://localhost:3100/loki/api/v1/query_range" --data-urlencode '
 
 ## `GET /loki/api/v1/labels`
 
-`/loki/api/v1/labels` retrieves the list of known labels within a given time span. It
-accepts the following query parameters in the URL:
+`/loki/api/v1/labels` retrieves the list of known labels within a given time span.
+Loki may use a larger time span than the one specified.
+It accepts the following query parameters in the URL:
 
 - `start`: The start time for the query as a nanosecond Unix epoch. Defaults to 6 hours ago.
 - `end`: The end time for the query as a nanosecond Unix epoch. Defaults to now.
@@ -424,8 +425,8 @@ $ curl -G -s  "http://localhost:3100/loki/api/v1/labels" | jq
 ## `GET /loki/api/v1/label/<name>/values`
 
 `/loki/api/v1/label/<name>/values` retrieves the list of known values for a given
-label within a given time span. It accepts the following query parameters in
-the URL:
+label within a given time span. Loki may use a larger time span than the one specified.
+It accepts the following query parameters in the URL:
 
 - `start`: The start time for the query as a nanosecond Unix epoch. Defaults to 6 hours ago.
 - `end`: The end time for the query as a nanosecond Unix epoch. Defaults to now.