Add docs for syndic_wait setting

Fixes #38174

conf/master

@@ -815,6 +815,10 @@
 # order will be used.
 #syndic_failover: random
 
+# The number of seconds for the salt client to wait for additional syndics to
+# check in with their lists of expected minions before giving up.
+#syndic_wait: 5
+
 
 #####      Peer Publish settings     #####
 ##########################################

doc/ref/configuration/master.rst

@@ -2982,6 +2982,20 @@ order will be used.
 
     syndic_failover: random
 
+.. conf_master:: syndic_wait
+
+``syndic_wait``
+---------------
+
+Default: ``5``
+
+The number of seconds for the salt client to wait for additional syndics to
+check in with their lists of expected minions before giving up.
+
+.. code-block:: yaml
+
+    syndic_wait: 5
+
 
 Peer Publish Settings
 =====================

doc/topics/topology/syndic.rst

@@ -168,6 +168,16 @@ daemon until the data reaches the Master or Syndic node that issued the command.
 Syndic wait
 ===========
 
+``syndic_wait`` is a master configuration file setting that specifies the number of
+seconds the Salt client should wait for additional syndics to check in with their
+lists of expected minions before giving up. This value defaults to ``5`` seconds.
+
+The ``syndic_wait`` setting is necessary because the higher-level master does not
+have a way of knowing which minions are below the syndics. The higher-level master
+has its own list of expected minions and the masters below them have their own lists
+as well, so the Salt client does not how long to wait for all returns. The
+``syndic_wait`` option allows time for all minions to return to the Salt client.
+
 .. note::
 
     To reduce the amount of time the CLI waits for Minions to respond, install