Index: firmware/App/Modes/ModeTreatment.c
===================================================================
diff -u -r51147222d369a3023a11b2ee675178d058ffaf46 -rd4850547b287cc1f94ea3617a1902c5278ea86b4
--- firmware/App/Modes/ModeTreatment.c	(.../ModeTreatment.c)	(revision 51147222d369a3023a11b2ee675178d058ffaf46)
+++ firmware/App/Modes/ModeTreatment.c	(.../ModeTreatment.c)	(revision d4850547b287cc1f94ea3617a1902c5278ea86b4)
@@ -40,6 +40,7 @@
 // ********** private definitions **********
 
 #define MAX_TREATMENT_TIME_MINUTES              ( 8 * MIN_PER_HOUR )                        ///< Maximum treatment time (in minutes).
+#define MIN_TREATMENT_TIME_MINUTES              ( 1 * MIN_PER_HOUR )                        ///< Minimum treatment time (in minutes).
 #define MAX_UF_RATE_ML_MIN                      ( (F32)2500 / (F32)MIN_PER_HOUR )           ///< Maximum ultrafiltration rate (in mL/min).
 #define MAX_UF_VOLUME_ML                        ( 8 * ML_PER_LITER )                        ///< Maximum ultrafiltration volume (in mL).
 #define MAX_DIALYSATE_VOLUME_ML                 ( 180 * ML_PER_LITER )                      ///< Maximum dialysate volume (in mL).
@@ -370,7 +371,7 @@
     // check if we are in an appropriate treatment state for settings adjustment
     if ( ( MODE_TREA == currMode ) &&
          ( currentTreatmentState > TREATMENT_START_STATE ) && ( currentTreatmentState < TREATMENT_DIALYSIS_END_STATE ) &&
-         ( CALC_ELAPSED_TREAT_TIME_IN_MIN() < treatmentTime ) )
+         ( CALC_ELAPSED_TREAT_TIME_IN_MIN() < treatmentTime ) && ( treatmentTime >= MIN_TREATMENT_TIME_MINUTES ) )
     {
         F32 uFVolume;
         U32 dialVolume = presDialysateFlowRate * treatmentTime;   // in mL
@@ -413,6 +414,10 @@
         {
             rejectReason = REQUEST_REJECT_REASON_INVALID_TREATMENT_STATE;
         }
+        else if ( treatmentTime < MIN_TREATMENT_TIME_MINUTES )
+        {
+            rejectReason = REQUEST_REJECT_REASON_TREATMENT_TIME_LESS_THAN_MINIMUM;
+        }
         else
         {
             rejectReason = REQUEST_REJECT_REASON_TREATMENT_TIME_LESS_THAN_CURRENT;
@@ -478,8 +483,9 @@
             pendingUFRateChange = uFRate;
             rateDiff = ( uFRate - presUFRate );
 
-            // verify treatment duration change would be valid
-            if ( ( trtTime <= MAX_TREATMENT_TIME_MINUTES ) && ( dialVolume <= MAX_DIALYSATE_VOLUME_ML ) )
+            // verify treatment duration change would be valid (leave zero if not valid - UI will disable option)
+            if ( ( trtTime <= MAX_TREATMENT_TIME_MINUTES ) && ( trtTime >= MIN_TREATMENT_TIME_MINUTES ) &&
+                 ( dialVolume <= MAX_DIALYSATE_VOLUME_ML ) )
             {
                 pendingTreatmentTimeChange = trtTime;
                 timeDiff = trtTime - ( (U32)( (F32)presTreatmentTimeSecs / (F32)SEC_PER_MIN ) + 1 );