Always remember to commit, lord.

code/__DEFINES/MC.dm

@@ -1,5 +1,7 @@
 #define MC_TICK_CHECK ( ( TICK_USAGE > Master.current_ticklimit || src.state != SS_RUNNING ) ? pause() : 0 )
 
+#define MC_TICK_REMAINING_MS ((Master.current_ticklimit - TICK_USAGE) * world.tick_lag)
+
 #define MC_SPLIT_TICK_INIT(phase_count) var/original_tick_limit = Master.current_ticklimit; var/split_tick_phases = ##phase_count
 #define MC_SPLIT_TICK \
 	if(split_tick_phases > 1){\

code/controllers/subsystem/air.dm

@@ -6,9 +6,7 @@ SUBSYSTEM_DEF(air)
 	flags = SS_BACKGROUND
 	runlevels = RUNLEVEL_GAME | RUNLEVEL_POSTGAME
 
-	var/cost_copy_from = 0
 	var/cost_turfs = 0
-	var/cost_copy_to = 0
 	var/cost_groups = 0
 	var/cost_highpressure = 0
 	var/cost_hotspots = 0
@@ -46,6 +44,7 @@ SUBSYSTEM_DEF(air)
 	msg += "C:{"
 	msg += "AT:[round(cost_turfs,1)]|"
 	msg += "TH:[round(turf_process_time(),1)]|"
+	msg += "EG:[round(cost_groups,1)]|"
 	msg += "EQ:[round(cost_equalize,1)]|"
 	msg += "HP:[round(cost_highpressure,1)]|"
 	msg += "HS:[round(cost_hotspots,1)]|"
@@ -121,6 +120,15 @@ SUBSYSTEM_DEF(air)
 		if(state != SS_RUNNING)
 			return
 		resumed = 0
+		currentpart = SSAIR_EXCITEDGROUPS
+
+	if(currentpart == SSAIR_EXCITEDGROUPS)
+		timer = TICK_USAGE_REAL
+		process_excited_groups(resumed)
+		cost_groups = MC_AVERAGE(cost_groups, TICK_DELTA_TO_MS(TICK_USAGE_REAL - timer))
+		if(state != SS_RUNNING)
+			return
+		resumed = 0
 		currentpart = SSAIR_HIGHPRESSURE
 
 	if(currentpart == SSAIR_HIGHPRESSURE)
@@ -278,8 +286,17 @@ SUBSYSTEM_DEF(air)
 			return
 	*/
 
+/proc/post_process_excited_turf(turf/open/T)
+	if(istype(T))
+		T.update_visuals()
+
+/datum/controller/subsystem/air/proc/process_excited_groups(resumed = 0)
+	if(!process_excited_groups_extools(CALLBACK(GLOBAL_PROC,/proc/post_process_excited_turf)))
+		pause()
+
 /datum/controller/subsystem/air/proc/process_turfs_extools()
 /datum/controller/subsystem/air/proc/process_turf_equalize_extools()
+/datum/controller/subsystem/air/proc/process_excited_groups_extools()
 /datum/controller/subsystem/air/proc/get_amt_gas_mixes()
 /datum/controller/subsystem/air/proc/get_max_gas_mixes()
 /datum/controller/subsystem/air/proc/turf_process_time()

code/controllers/subsystem/callback.dm

@@ -9,5 +9,12 @@ SUBSYSTEM_DEF(callbacks)
 	SScallbacks.flags |= SS_NO_FIRE
 	CRASH("Auxtools not found! Callback subsystem shutting itself off.")
 
+/proc/_process_callbacks_priority()
+	SScallbacks.can_fire = 0
+	SScallbacks.flags |= SS_NO_FIRE
+	CRASH("Auxtools not found! Callback subsystem shutting itself off.")
+
 /datum/controller/subsystem/callbacks/fire()
-	_process_callbacks()
+	_process_callbacks_priority()
+	if(TICK_CHECK || _process_callbacks(MC_TICK_REMAINING_MS))
+		pause()

tgstation.dme

@@ -298,7 +298,6 @@
 #include "code\controllers\subsystem\acid.dm"
 #include "code\controllers\subsystem\adjacent_air.dm"
 #include "code\controllers\subsystem\air.dm"
-#include "code\controllers\subsystem\air_turfs.dm"
 #include "code\controllers\subsystem\assets.dm"
 #include "code\controllers\subsystem\atoms.dm"
 #include "code\controllers\subsystem\augury.dm"