update balances mirror node api

Author: theekrystallee

sdks-and-apis/rest-api/balances.md

@@ -24,6 +24,12 @@ Each **balance object** includes:
 * **Balance (in HBAR)** – The most recent balance available.
 * **Token Balances (if applicable)** – Associated token balances for the account.
 
+{% hint style="info" %}
+#### Note
+
+Balance information returned by this API has a 15 minute granularity when using the `timestamp` query parameter, as it's generated by an asynchronous balance snapshot process. When not using the `timestamp` parameter, the API returns real-time balance data.
+{% endhint %}
+
 {% openapi-operation spec="mainnet" path="/api/v1/balances" method="get" %}
 [Broken link](broken-reference)
 {% endopenapi-operation %}