diff --git a/tests/nexus/platform/nexus_node.cpp b/tests/nexus/platform/nexus_node.cpp
index de048d2bb..c2bc0d1de 100644
--- a/tests/nexus/platform/nexus_node.cpp
+++ b/tests/nexus/platform/nexus_node.cpp
@@ -87,15 +87,6 @@ void Node::Join(Node &aNode, JoinMode aJoinMode)
         break;
     case kAsSed:
         break;
-    case kAsSsed:
-    {
-        static constexpr uint32_t kDefaultCslPeriod  = 100 * 1000 / OT_US_PER_TEN_SYMBOLS; // 100 ms
-        static constexpr uint32_t kDefaultCslTimeout = 30;                                 // 30 seconds
-
-        Get<Mac::Mac>().SetCslPeriod(kDefaultCslPeriod);
-        Get<Mle::Mle>().SetCslTimeout(kDefaultCslTimeout);
-        break;
-    }
     }
 
     SuccessOrQuit(Get<Mle::Mle>().SetDeviceMode(Mle::DeviceMode(mode)));
diff --git a/tests/nexus/platform/nexus_node.hpp b/tests/nexus/platform/nexus_node.hpp
index 6aaa9a2aa..95cfc3ba9 100644
--- a/tests/nexus/platform/nexus_node.hpp
+++ b/tests/nexus/platform/nexus_node.hpp
@@ -79,7 +79,6 @@ public:
         kAsFed,
         kAsMed,
         kAsSed,
-        kAsSsed,
         kAsSedWithFullNetData,
     };
 
diff --git a/tests/nexus/test_1_2_LP_5_3_1.cpp b/tests/nexus/test_1_2_LP_5_3_1.cpp
index abd6b32a2..4edcb1a8d 100644
--- a/tests/nexus/test_1_2_LP_5_3_1.cpp
+++ b/tests/nexus/test_1_2_LP_5_3_1.cpp
@@ -49,6 +49,21 @@ static constexpr uint32_t kAttachToRouterTime = 200 * 1000;
  */
 static constexpr uint32_t kAttachAsSsedTime = 20 * 1000;
 
+/**
+ * CSL Period in milliseconds.
+ */
+static constexpr uint32_t kCslPeriodMs = 100;
+
+/**
+ * CSL Period in units of 10 symbols.
+ */
+static constexpr uint32_t kCslPeriod = kCslPeriodMs * 1000 / OT_US_PER_TEN_SYMBOLS;
+
+/**
+ * Time to advance for CSL synchronization to complete, in milliseconds.
+ */
+static constexpr uint32_t kCslSyncTime = 5 * 1000;
+
 /**
  * Payload size for a standard ICMPv6 Echo Request.
  */
@@ -121,7 +136,11 @@ void Test1_2_LP_5_3_1(void)
      * - Pass Criteria: N/A.
      */
 
-    ssed1.Join(leader, Node::kAsSsed);
+    ssed1.Join(leader, Node::kAsSed);
+    nexus.AdvanceTime(kAttachAsSsedTime);
+    VerifyOrQuit(ssed1.Get<Mle::Mle>().IsAttached());
+
+    ssed1.Get<Mac::Mac>().SetCslPeriod(kCslPeriod);
 
     Log("---------------------------------------------------------------------------------------");
     Log("Step 3: Leader (DUT)");
@@ -134,8 +153,8 @@ void Test1_2_LP_5_3_1(void)
      *   - The Frame Version of the packet MUST be: IEEE Std 802.15.4-2015 (value = 0b10).
      */
 
-    nexus.AdvanceTime(kAttachAsSsedTime);
-    VerifyOrQuit(ssed1.Get<Mle::Mle>().IsAttached());
+    nexus.AdvanceTime(kCslSyncTime);
+    VerifyOrQuit(ssed1.Get<Mac::Mac>().IsCslEnabled());
 
     Log("---------------------------------------------------------------------------------------");
     Log("Step 4: Router_1");
diff --git a/tests/nexus/verify_1_2_LP_5_3_1.py b/tests/nexus/verify_1_2_LP_5_3_1.py
index e00e6be3e..2bc02a50f 100644
--- a/tests/nexus/verify_1_2_LP_5_3_1.py
+++ b/tests/nexus/verify_1_2_LP_5_3_1.py
@@ -61,6 +61,7 @@ def verify(pv):
     LEADER = pv.vars['LEADER']
     LEADER_RLOC16 = pv.vars['LEADER_RLOC16']
     ROUTER_1 = pv.vars['ROUTER_1']
+    ROUTER_1_RLOC16 = pv.vars['ROUTER_1_RLOC16']
     SSED_1 = pv.vars['SSED_1']
     SSED_1_RLOC16 = pv.vars['SSED_1_RLOC16']
 
@@ -89,10 +90,10 @@ def verify(pv):
     #   - The Frame Version of the packet MUST be: IEEE Std 802.15.4-2015 (value = 0b10).
     print("Step 3: Leader completes CSL connection")
 
-    pkts.filter_wpan_src64(LEADER).\
+    _response_pkt = pkts.filter_wpan_src64(LEADER).\
         filter_wpan_dst64(SSED_1).\
         filter_mle_cmd(consts.MLE_CHILD_UPDATE_RESPONSE).\
-        filter(lambda p: p.wpan.version == 2).\
+        filter(lambda p: p.wpan.version == consts.MAC_FRAME_VERSION_2015).\
         must_next()
 
     # Step 4: Router_1
@@ -105,26 +106,38 @@ def verify(pv):
     #   - Router_1 MUST receive an ICMPv6 Echo Response from SSED_1.
     print("Step 4: Router_1 sends Echo Request to SSED_1")
 
+    # Echo Request from ROUTER_1 to LEADER
+    pkts.filter_ping_request().\
+        filter_wpan_src64(ROUTER_1).\
+        filter_wpan_dst16(LEADER_RLOC16).\
+        must_next()
+
     # Forwarded Echo Request from LEADER to SSED_1
     _pkt = pkts.filter_ping_request().\
         filter_wpan_src64(LEADER).\
         filter_wpan_dst16(SSED_1_RLOC16).\
-        filter(lambda p: p.wpan.version == 2).\
+        filter(lambda p: p.wpan.version == consts.MAC_FRAME_VERSION_2015).\
         must_next()
 
     # SSED_1 MUST NOT send a MAC Data Request prior to receiving the ICMPv6 Echo Request from the Leader.
-    pkts.range((0, 0), (_pkt.number, _pkt.number)).\
+    pkts.range((_response_pkt.number, _response_pkt.number), (_pkt.number, _pkt.number)).\
         filter_wpan_src64(SSED_1).\
         filter_wpan_dst16(LEADER_RLOC16).\
         filter_wpan_cmd(consts.WPAN_DATA_REQUEST).\
         must_not_next()
 
-    # Echo Response from SSED_1 to ROUTER_1
+    # Echo Response from SSED_1 to LEADER
     pkts.filter_ping_reply(identifier=_pkt.icmpv6.echo.identifier).\
         filter_wpan_src64(SSED_1).\
         filter_wpan_dst16(LEADER_RLOC16).\
         must_next()
 
+    # Forwarded Echo Response from LEADER to ROUTER_1
+    pkts.filter_ping_reply(identifier=_pkt.icmpv6.echo.identifier).\
+        filter_wpan_src64(LEADER).\
+        filter_wpan_dst16(ROUTER_1_RLOC16).\
+        must_next()
+
 
 if __name__ == '__main__':
     verify_utils.run_main(verify)