diff --git a/include/siirtc.h b/include/siirtc.h
index de4fd634df..24573e4429 100644
--- a/include/siirtc.h
+++ b/include/siirtc.h
@@ -9,6 +9,10 @@
 #define SIIRTCINFO_24HOUR 0x40 // 0: 12-hour mode, 1: 24-hour mode
 #define SIIRTCINFO_POWER  0x80 // power on or power failure occurred
 
+#define DAY_HOURS       24
+#define HOUR_MINUTES    60
+#define MINUTE_SECONDS  60
+
 enum
 {
     MONTH_JAN = 1,
@@ -22,7 +26,8 @@ enum
     MONTH_SEP,
     MONTH_OCT,
     MONTH_NOV,
-    MONTH_DEC
+    MONTH_DEC,
+    MONTH_COUNT = MONTH_DEC
 };
 
 struct SiiRtcInfo
diff --git a/src/pokemon.c b/src/pokemon.c
index 7bc9f3bee3..fe93c14c19 100644
--- a/src/pokemon.c
+++ b/src/pokemon.c
@@ -48,6 +48,12 @@
 #include "constants/trainers.h"
 #include "constants/union_room.h"
 
+#define DAY_EVO_HOUR_BEGIN   12
+#define DAY_EVO_HOUR_END     DAY_HOURS
+
+#define NIGHT_EVO_HOUR_BEGIN 0
+#define NIGHT_EVO_HOUR_END   12
+
 struct SpeciesItem
 {
     u16 species;
@@ -5498,12 +5504,12 @@ u16 GetEvolutionTargetSpecies(struct Pokemon *mon, u8 mode, u16 evolutionItem)
                 break;
             case EVO_FRIENDSHIP_DAY:
                 RtcCalcLocalTime();
-                if (gLocalTime.hours >= 12 && gLocalTime.hours < 24 && friendship >= 220)
+                if (gLocalTime.hours >= DAY_EVO_HOUR_BEGIN && gLocalTime.hours < DAY_EVO_HOUR_END && friendship >= 220)
                     targetSpecies = gEvolutionTable[species][i].targetSpecies;
                 break;
             case EVO_FRIENDSHIP_NIGHT:
                 RtcCalcLocalTime();
-                if (gLocalTime.hours >= 0 && gLocalTime.hours < 12 && friendship >= 220)
+                if (gLocalTime.hours >= NIGHT_EVO_HOUR_BEGIN && gLocalTime.hours < NIGHT_EVO_HOUR_END && friendship >= 220)
                     targetSpecies = gEvolutionTable[species][i].targetSpecies;
                 break;
             case EVO_LEVEL:
diff --git a/src/rtc.c b/src/rtc.c
index b135a675a8..a4920025cf 100644
--- a/src/rtc.c
+++ b/src/rtc.c
@@ -16,20 +16,20 @@ struct Time gLocalTime;
 
 static const struct SiiRtcInfo sRtcDummy = {0, MONTH_JAN, 1}; // 2000 Jan 1
 
-static const s32 sNumDaysInMonths[12] =
+static const s32 sNumDaysInMonths[MONTH_COUNT] =
 {
-    31,
-    28,
-    31,
-    30,
-    31,
-    30,
-    31,
-    31,
-    30,
-    31,
-    30,
-    31,
+    [MONTH_JAN - 1] = 31,
+    [MONTH_FEB - 1] = 28,
+    [MONTH_MAR - 1] = 31,
+    [MONTH_APR - 1] = 30,
+    [MONTH_MAY - 1] = 31,
+    [MONTH_JUN - 1] = 30,
+    [MONTH_JUL - 1] = 31,
+    [MONTH_AUG - 1] = 31,
+    [MONTH_SEP - 1] = 30,
+    [MONTH_OCT - 1] = 31,
+    [MONTH_NOV - 1] = 30,
+    [MONTH_DEC - 1] = 31,
 };
 
 void RtcDisableInterrupts(void)
@@ -171,7 +171,7 @@ u16 RtcCheckInfo(struct SiiRtcInfo *rtc)
 
     month = ConvertBcdToBinary(rtc->month);
 
-    if (month == 0xFF || month == 0 || month > 12)
+    if (month == 0xFF || month == 0 || month > MONTH_COUNT)
         errorFlags |= RTC_ERR_INVALID_MONTH;
 
     value = ConvertBcdToBinary(rtc->day);
@@ -192,17 +192,17 @@ u16 RtcCheckInfo(struct SiiRtcInfo *rtc)
 
     value = ConvertBcdToBinary(rtc->hour);
 
-    if (value > 24)
+    if (value > DAY_HOURS)
         errorFlags |= RTC_ERR_INVALID_HOUR;
 
     value = ConvertBcdToBinary(rtc->minute);
 
-    if (value > 60)
+    if (value > HOUR_MINUTES)
         errorFlags |= RTC_ERR_INVALID_MINUTE;
 
     value = ConvertBcdToBinary(rtc->second);
 
-    if (value > 60)
+    if (value > MINUTE_SECONDS)
         errorFlags |= RTC_ERR_INVALID_SECOND;
 
     return errorFlags;
@@ -270,19 +270,19 @@ void RtcCalcTimeDifference(struct SiiRtcInfo *rtc, struct Time *result, struct T
 
     if (result->seconds < 0)
     {
-        result->seconds += 60;
+        result->seconds += MINUTE_SECONDS;
         --result->minutes;
     }
 
     if (result->minutes < 0)
     {
-        result->minutes += 60;
+        result->minutes += HOUR_MINUTES;
         --result->hours;
     }
 
     if (result->hours < 0)
     {
-        result->hours += 24;
+        result->hours += DAY_HOURS;
         --result->days;
     }
 }
@@ -317,19 +317,19 @@ void CalcTimeDifference(struct Time *result, struct Time *t1, struct Time *t2)
 
     if (result->seconds < 0)
     {
-        result->seconds += 60;
+        result->seconds += MINUTE_SECONDS;
         --result->minutes;
     }
 
     if (result->minutes < 0)
     {
-        result->minutes += 60;
+        result->minutes += HOUR_MINUTES;
         --result->hours;
     }
 
     if (result->hours < 0)
     {
-        result->hours += 24;
+        result->hours += DAY_HOURS;
         --result->days;
     }
 }
@@ -337,7 +337,7 @@ void CalcTimeDifference(struct Time *result, struct Time *t1, struct Time *t2)
 u32 RtcGetMinuteCount(void)
 {
     RtcGetInfo(&sRtc);
-    return (24 * 60) * RtcGetDayCount(&sRtc) + 60 * sRtc.hour + sRtc.minute;
+    return (DAY_HOURS * HOUR_MINUTES) * RtcGetDayCount(&sRtc) + HOUR_MINUTES * sRtc.hour + sRtc.minute;
 }
 
 u32 RtcGetLocalDayCount(void)