diff --git a/init.lua b/init.lua
index 8774bc9..53fb010 100644
--- a/init.lua
+++ b/init.lua
@@ -49,4 +49,5 @@ if minetest.get_modpath("mtt") and mtt.enabled then
 	dofile(MP .. "/conditions.spec.lua")
 	dofile(MP .. "/build.spec.lua")
 	dofile(MP .. "/build_over.spec.lua")
+	dofile(MP .. "/timer.spec.lua")
 end
diff --git a/timer.lua b/timer.lua
index dab54ed..2a732e6 100644
--- a/timer.lua
+++ b/timer.lua
@@ -11,36 +11,40 @@ function building_lib.get_building_timer(mapblock_pos)
     return setmetatable(self, BuildingTimer_mt)
 end
 
-local function get_timer_key(mapblock_pos)
-    return "timer_" .. minetest.pos_to_string(mapblock_pos)
-end
-
 function BuildingTimer:get_entry()
     local data = building_lib.store:get_group_data(self.mapblock_pos)
-    local key = get_timer_key(self.mapblock_pos)
-    return data[key] or {}
+    if not data.timers then
+        -- create timers table
+        data.timers = {}
+        building_lib.store:set_group_data(self.mapblock_pos, data)
+    end
+
+    local key = minetest.pos_to_string(self.mapblock_pos)
+    return data.timers[key] or {}
+end
+
+function BuildingTimer:set_entry(entry)
+    local data = building_lib.store:get_group_data(self.mapblock_pos)
+    if not data.timers then
+        -- create timers table
+        data.timers = {}
+    end
+
+    local key = minetest.pos_to_string(self.mapblock_pos)
+    data.timers[key] = entry
+    building_lib.store:set_group_data(self.mapblock_pos, data)
 end
 
 function BuildingTimer:set(timeout, elapsed)
-    -- TODO: move timers to own field for better lookup
-    local data = building_lib.store:get_group_data(self.mapblock_pos)
-    local key = get_timer_key(self.mapblock_pos)
-
     if timeout > 0 then
-        -- started, update entry
-        local entry = data[key]
-        if not entry then
-            entry = {}
-            data[key] = entry
-        end
-
-        entry.timeout = timeout
-        entry.elapsed = elapsed
+        self:set_entry({
+            timeout = timeout,
+            elapsed = elapsed
+        })
     else
         -- stopped, remove entry
-        data[key] = nil
+        self:set_entry(nil)
     end
-    building_lib.store:set_group_data(self.mapblock_pos, data)
 end
 
 function BuildingTimer:start(timeout)
@@ -66,12 +70,52 @@ function BuildingTimer:is_started()
     return entry.timeout and entry.timeout > entry.elapsed
 end
 
-function building_lib.update_timers(pos)
-    -- TODO
-    print(dump(pos))
+function building_lib.update_timers(pos, interval)
+    local rpos = mapblock_lib.get_mapblock(pos)
+    local data = building_lib.store:get_group_data(rpos)
+
+    if not data.timers then
+        -- no timers found in the mapblock
+        return
+    end
+
+    for mapblock_pos_str, entry in pairs(data.timers) do
+        -- increment active timers and call `on_timer` on buildings
+        local mapblock_pos = minetest.string_to_pos(mapblock_pos_str)
+        entry.elapsed = entry.elapsed + interval
+
+        local remove_timer = false
+
+        if entry.elapsed >= entry.timeout then
+            -- timer event
+            local def = building_lib.get_building_def_at(mapblock_pos)
+            if type(def.on_timer) == "function" then
+                local result = def.on_timer(mapblock_pos, entry.elapsed)
+                if result then
+                    -- reschedule
+                    entry.elapsed = 0
+                else
+                    -- remove
+                    remove_timer = true
+                end
+            else
+                -- invalid field type
+                remove_timer = true
+            end
+        end
+
+        if remove_timer then
+            data.timers[mapblock_pos_str] = nil
+        end
+    end
+
+    -- store timer data
+    building_lib.store:set_group_data(rpos, data)
 end
 
--- TODO: iterate over active areas and operate on `DataStorage:get_group_data(pos)`
+local TIMER_INTERVAL = 2
+
+-- iterate over active areas and operate on `DataStorage:get_group_data(pos)`
 local function timer_update_loop()
     local visited = {}
 
@@ -93,7 +137,7 @@ local function timer_update_loop()
 
                     -- check if already processed
                     if not visited[key] then
-                        building_lib.update_timers(pos)
+                        building_lib.update_timers(pos, TIMER_INTERVAL)
                         visited[key] = true
                     end
                 end
@@ -101,7 +145,7 @@ local function timer_update_loop()
         end
     end
 
-    minetest.after(2, timer_update_loop)
+    minetest.after(TIMER_INTERVAL, timer_update_loop)
 end
 
 minetest.after(1, timer_update_loop)
diff --git a/timer.spec.lua b/timer.spec.lua
new file mode 100644
index 0000000..6712c98
--- /dev/null
+++ b/timer.spec.lua
@@ -0,0 +1,41 @@
+
+local building_mapblock_pos = {x=0, y=0, z=0}
+local building_name = "building_lib:dummy_timer"
+local rotation = 0
+local playername = "singleplayer"
+
+local timer_mapblock_pos, timer_elapsed
+
+building_lib.register_building(building_name, {
+	placement = "dummy",
+    on_timer = function(mapblock_pos, elapsed)
+        timer_mapblock_pos = mapblock_pos
+        timer_elapsed = elapsed
+    end
+})
+
+mtt.register("building_lib.get_building_timer", function()
+    -- clear store
+    building_lib.store:clear()
+
+    -- try to build
+    local success, err = building_lib.can_build(building_mapblock_pos, playername, building_name, rotation)
+    assert(not err)
+    assert(success)
+
+    -- build
+    return building_lib.build(building_mapblock_pos, playername, building_name, rotation)
+    :next(function()
+        local timer = building_lib.get_building_timer(building_mapblock_pos)
+        timer:start(10)
+
+        local pos = { x=0, y=0, z=0 }
+        building_lib.update_timers(pos, 5)
+        assert(not timer_mapblock_pos)
+        assert(not timer_elapsed)
+
+        building_lib.update_timers(pos, 5)
+        assert(vector.equals(timer_mapblock_pos, building_mapblock_pos))
+        assert(timer_elapsed >= 10)
+    end)
+end)