diff --git a/modules/cfe_testcase/CMakeLists.txt b/modules/cfe_testcase/CMakeLists.txt
index 6dc8e4918..02c28a9bc 100644
--- a/modules/cfe_testcase/CMakeLists.txt
+++ b/modules/cfe_testcase/CMakeLists.txt
@@ -28,6 +28,7 @@ add_cfe_app(cfe_testcase
     src/time_arithmetic_test.c
     src/time_current_test.c
     src/time_conversion_test.c
+    src/time_external_test.c
     src/time_misc_test.c
 )
 
diff --git a/modules/cfe_testcase/src/cfe_test.c b/modules/cfe_testcase/src/cfe_test.c
index c1faaaa4e..78a94ad38 100644
--- a/modules/cfe_testcase/src/cfe_test.c
+++ b/modules/cfe_testcase/src/cfe_test.c
@@ -81,6 +81,7 @@ void CFE_TestMain(void)
     TimeArithmeticTestSetup();
     TimeConversionTestSetup();
     TimeCurrentTestSetup();
+    TimeExternalTestSetup();
     TimeMiscTestSetup();
 
     /*
diff --git a/modules/cfe_testcase/src/cfe_test.h b/modules/cfe_testcase/src/cfe_test.h
index 591193e17..af5db13dc 100644
--- a/modules/cfe_testcase/src/cfe_test.h
+++ b/modules/cfe_testcase/src/cfe_test.h
@@ -116,6 +116,7 @@ void TBLRegistrationTestSetup(void);
 void TimeArithmeticTestSetup(void);
 void TimeConversionTestSetup(void);
 void TimeCurrentTestSetup(void);
+void TimeExternalTestSetup(void);
 void TimeMiscTestSetup(void);
 
 #endif /* CFE_TEST_H */
diff --git a/modules/cfe_testcase/src/time_external_test.c b/modules/cfe_testcase/src/time_external_test.c
new file mode 100644
index 000000000..467cf9226
--- /dev/null
+++ b/modules/cfe_testcase/src/time_external_test.c
@@ -0,0 +1,104 @@
+/*************************************************************************
+**
+**      GSC-18128-1, "Core Flight Executive Version 6.7"
+**
+**      Copyright (c) 2006-2019 United States Government as represented by
+**      the Administrator of the National Aeronautics and Space Administration.
+**      All Rights Reserved.
+**
+**      Licensed under the Apache License, Version 2.0 (the "License");
+**      you may not use this file except in compliance with the License.
+**      You may obtain a copy of the License at
+**
+**        http://www.apache.org/licenses/LICENSE-2.0
+**
+**      Unless required by applicable law or agreed to in writing, software
+**      distributed under the License is distributed on an "AS IS" BASIS,
+**      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+**      See the License for the specific language governing permissions and
+**      limitations under the License.
+**
+** File: time_external_test.c
+**
+** Purpose:
+**   Functional test of basic External Time Source APIs
+**
+**   Demonstration of how to register and use the UT assert functions.
+**
+*************************************************************************/
+
+/*
+ * Includes
+ */
+
+#include "cfe_test.h"
+
+int32 TestCallbackFunction(void)
+{
+    CFE_FT_Global.Count += 1;
+    return CFE_SUCCESS;
+}
+
+int32 TestCallbackFunction2(void)
+{
+    CFE_FT_Global.Count = 0;
+    return CFE_SUCCESS;
+}
+
+void TestCallback(void)
+{
+    CFE_FT_Global.Count = 1;
+
+    UtPrintf("Testing: CFE_TIME_RegisterSynchCallback, CFE_TIME_UnregisterSynchCallback");
+
+    UtAssert_INT32_EQ(CFE_TIME_RegisterSynchCallback(&TestCallbackFunction), CFE_SUCCESS);
+    UtAssert_INT32_EQ(CFE_TIME_RegisterSynchCallback(&TestCallbackFunction2), CFE_TIME_TOO_MANY_SYNCH_CALLBACKS);
+
+    OS_TaskDelay(2500);
+    if (CFE_FT_Global.Count < 2)
+    {
+        UtAssert_MIR("CFE_TIME_RegisterSynchCallback requires manual inspection to determine if failure is with the "
+                     "API or due to an insufficient timing performance of this machine");
+    }
+
+    CFE_FT_Global.Count = 1;
+    UtAssert_INT32_EQ(CFE_TIME_UnregisterSynchCallback(&TestCallbackFunction), CFE_SUCCESS);
+    UtAssert_INT32_EQ(CFE_TIME_UnregisterSynchCallback(&TestCallbackFunction), CFE_TIME_CALLBACK_NOT_REGISTERED);
+
+    OS_TaskDelay(2500);
+    UtAssert_INT32_LTEQ(CFE_FT_Global.Count, 2);
+
+    UtAssert_INT32_EQ(CFE_TIME_UnregisterSynchCallback(NULL), CFE_TIME_BAD_ARGUMENT);
+    UtAssert_INT32_EQ(CFE_TIME_RegisterSynchCallback(NULL), CFE_TIME_BAD_ARGUMENT);
+}
+
+void TestExternal(void)
+{
+#if ((CFE_PLATFORM_TIME_CFG_SRC_MET == true) || (CFE_PLATFORM_TIME_CFG_SRC_GPS == true) || \
+     (CFE_PLATFORM_TIME_CFG_SRC_TIME == true))
+    CFE_TIME_SysTime_t time = {1000, 0};
+#endif
+
+    UtPrintf("Testing: CFE_TIME_ExternalTone, CFE_TIME_ExternalMET, CFE_TIME_ExternalGPS, CFE_TIME_ExternalTime");
+    /* These time calls could impact the system timekeeping. Likely impact is incorrect time for one update cycle, a
+     * rejected external time update, multiple tone's or external updates detected, or similar. */
+    UtAssert_VOIDCALL(CFE_TIME_ExternalTone());
+
+#if (CFE_PLATFORM_TIME_CFG_SRC_MET == true)
+    UtAssert_VOIDCALL(CFE_TIME_ExternalMET(time));
+#endif
+
+#if (CFE_PLATFORM_TIME_CFG_SRC_GPS == true)
+    UtAssert_VOIDCALL(CFE_TIME_ExternalGPS(time, 5));
+#endif
+
+#if (CFE_PLATFORM_TIME_CFG_SRC_TIME == true)
+    UtAssert_VOIDCALL(CFE_TIME_ExternalTime(time));
+#endif
+}
+
+void TimeExternalTestSetup(void)
+{
+    UtTest_Add(TestCallback, NULL, NULL, "Test Time Synch Callbacks");
+    UtTest_Add(TestExternal, NULL, NULL, "Test External Sources");
+}