The documentation for timer says the following:
:initial-delay Delay, in milliseconds, of first call. Defaults to 0.
It should read:
:initial-delay Delay, in milliseconds, of first call. Defaults to 1000.
(defn test-timer 
(let [p (promise)
t (timer (fn [_] (deliver p true))
Address issue #126
Initial delay for a timer was inexplicably set to 1000 rather than 0
Fixed. Thanks for noticing that.