diff --git a/ReadMe.md b/ReadMe.md
index 33c5d36..f4e1dd7 100644
--- a/ReadMe.md
+++ b/ReadMe.md
@@ -9,24 +9,29 @@ but that misses the biggest benefit, which is the timer library itself managing
 timers, including discarding expired timers:
 
 ```lua
-timer.after(time, function, ...) -- runs once after time
-timer.every(time, function, ...) -- runs repeatedly, every time
+timer.after(deadline, function, ...) -- runs once after time
+timer.every(interval, function, ...) -- runs repeatedly, every time
 
 timer.update(delta)              -- increment, run functions, discard expired..
 ```
 
+Functions are completely optional, so you can use the mechanism to track time
+rather than execute functions. `timer:get_run_time()` returns the amount of time
+since the last interval. (Note: This is only useful for repeating timers.
+One-run timers will only count to their `deadline` once, unless manually run.)
+
 A timer can be excluded from `timer.update`, in which case it must be manually
 updated:
 ```lua
-local my_timer = timer.every(time, function, ...)
-my_timer.manual = true
+local my_timer = timer.every(interval, function, ...)
+my_timer:set_manual(true)
 
 my_timer:update(delta)
 ```
 
 `timer.update` returns a table of expired timers. Example:
 ```lua
-local my_timer = timer.after(time, function, ...)
+local my_timer = timer.after(deadline, function, ...)
 
 local expired = timer.update(delta)
 if expired[my_timer] then
@@ -34,16 +39,22 @@ if expired[my_timer] then
 end
 ```
 
-Timers can have their time set to a new value with `my_timer:reset(time)`. If
-nothing is passed, they will be set to `0`.
+Timers can have their run time set to a new value with `my_timer:reset(time)`.
+If nothing is passed, they will be set to `0`.
+
+- One-run timers can have their `deadline` changed with
+  `my_timer:set_deadline(time)`.
+- Repeating timers can have their `interval` changed with
+  `my_timer:set_interval(time)`.
+- You can get deadlines/intervals with
+  `my_timer:get_deadline()` / `my_timer:get_interval()`.
 
 ---
 
 Incompatibilities / Changes from kikito's cron.lua:
-- Number values are not checked or restricted.
-- Different error message for callback not being callable.
-- If a one-time timer is run by `timer.update`, it will *no longer be updated*
-  by `timer.update`, even if reset.
+- There are no checks or restrictions on what can be set.
+- If a one-run timer is run by `timer.update`, it will *no longer be updated* by
+  `timer.update`, even if reset.
 
 ## Releases
 GitHub unpublishes my releases frequently, check tags to find them!
@@ -51,5 +62,5 @@ GitHub unpublishes my releases frequently, check tags to find them!
 ## Ideas / Tasks
 - [ ] Make an import/export format and add save/load functions - resumable timers.
   - [ ] Make it possible to save/load with a unix timestamp. (Dangerous.)
-- [ ] Make an access function `get_run_time`
-- [ ] Make functions optional
+- [x] Make an access function `get_run_time`
+- [x] Make functions optional
diff --git a/timer.lua b/timer.lua
index eada69e..aa6ab3d 100644
--- a/timer.lua
+++ b/timer.lua
@@ -1,17 +1,12 @@
-local is_callable = function(callback)
-  local _type = type(callback)
-  if _type == "function" then return true end
-  if _type == "table" then
-    local metatable = getmetatable(callback)
-    return (type(metatable) == "table") and (type(metatable.__call) == "function")
-  end
-end
+-- This file is public domain. Created by Tangent, the fox, the legend.
 
 local update_after = function(self, delta)
   if self.run_time >= self.deadline then return true end
   self.run_time = self.run_time + delta
   if self.run_time >= self.deadline then
-    self.callback(unpack(self.args))
+    if self.callback then
+      self.callback(unpack(self.args))
+    end
     return true
   end
 end
@@ -19,24 +14,48 @@ end
 local update_every = function(self, delta)
   self.run_time = self.run_time + delta
   while self.run_time >= self.interval do
-    self.callback(unpack(self.args))
+    if self.callback then
+      self.callback(unpack(self.args))
+    end
     self.run_time = self.run_time - self.interval
   end
 end
 
 local timer_metatable = {
   __index = {
+    get_deadline = function(self)
+      return self.deadline
+    end,
+    get_interval = function(self)
+      return self.interval
+    end,
+    get_run_time = function(self)
+      return self.run_time
+    end,
     reset = function(self, time)
       self.run_time = time or 0
     end,
+    set_deadline = function(self, deadline)
+      assert(self.deadline, "set_deadline() is only for timer.after() timers.")
+      self.deadline = deadline
+    end,
+    set_interval = function(self, interval)
+      assert(self.interval, "set_interval() is only for timer.every() timers.")
+      self.interval = interval
+    end,
+    set_manual = function(self, manual)
+      if manual then
+        self.manual = true
+      else
+        self.manual = nil
+      end
+    end,
   },
 }
 
 local timers = {}
 
 local new_timer = function(callback, update, ...)
-  assert(is_callable(callback), "callback function must be callable")
-
   local timer = setmetatable({
     callback = callback,
     update = update,
@@ -49,7 +68,7 @@ local new_timer = function(callback, update, ...)
 end
 
 return {
-  version = "v1.1.0",
+  version = "v1.2.0",
   after = function(deadline, callback, ...)
     local timer = new_timer(callback, update_after, ...)
     timer.deadline = deadline