diff --git a/engine/overworld/time.asm b/engine/overworld/time.asm
index dfb2632b0..2003910b3 100644
--- a/engine/overworld/time.asm
+++ b/engine/overworld/time.asm
@@ -390,7 +390,7 @@ _CalcHoursDaysSince:
 	ld c, a
 	sbc [hl]
 	jr nc, .skip
-	add 24
+	add MAX_HOUR
 .skip
 	ld [hl], c ; current hours
 	dec hl
diff --git a/engine/pokegear/pokegear.asm b/engine/pokegear/pokegear.asm
index d3d270bc9..5fa3a1ff0 100644
--- a/engine/pokegear/pokegear.asm
+++ b/engine/pokegear/pokegear.asm
@@ -1271,9 +1271,9 @@ PokegearPhoneContactSubmenu:
 
 GetAMPMHours: ; unreferenced
 	ldh a, [hHours]
-	cp 12
+	cp NOON_HOUR
 	jr c, .am
-	sub 12
+	sub NOON_HOUR
 	ld [wTempByteValue], a
 	scf
 	ret
diff --git a/mobile/mobile_40.asm b/mobile/mobile_40.asm
index 5b287adc5..101df6d59 100644
--- a/mobile/mobile_40.asm
+++ b/mobile/mobile_40.asm
@@ -1083,7 +1083,7 @@ Function1006dc:
 	ldh a, [hHours]
 	sbc c
 	jr nc, .asm_1006fb
-	add $18
+	add MAX_HOUR
 
 .asm_1006fb
 	ld [de], a