Does mixing Implicit and Explicit waits cause inconsistent timeout behavior?

Answer at a Glance

Yes. When an ImplicitWait is set on the driver and a WebDriverWait (explicit wait) is used for an element, the two mechanisms can interact in a way that makes the overall timeout longer than expected or inconsistent across driver implementations.

Confirmed Facts

• Implicit waits are handled by the browser driver (remote end) and apply to every element lookup.
• Explicit waits are evaluated by the language binding (client end) and poll the DOM until a condition or a timeout is reached.
• When an element is absent, the implicit wait can trigger first, causing the driver to pause for the full implicit duration before the explicit poll cycle starts.
• The resulting wait time is not simply the sum of both timeouts; it can exceed the explicit timeout and vary by driver.
• ChromeDriver, GeckoDriver, EdgeDriver, and SafariDriver exhibit different polling strategies, so the effect can differ between browsers.

Likely Explanation

Implicit waits are essentially a blanket retry mechanism: the driver will retry locating an element for the configured period. Explicit waits wrap a condition and poll the page at a configurable interval. When both are active, the implicit retry can “steal” time from the explicit wait’s polling loop. For example, with a 10‑second implicit wait and a 10‑second explicit wait on a missing element, the first lookup may block for 10 seconds, then the explicit wait starts its own polling cycle, potentially adding another 10 seconds before a TimeoutException is thrown.

Practical Steps

1. Measure the actual timeout:

   import time
   start = time.time()
   try:
       driver.implicitly_wait(10)
       WebDriverWait(driver, 10).until(EC.presence_of_element_located((By.ID, 'missing')))
   except TimeoutException:
       pass
   print(f"Elapsed: {time.time() - start:.2f}s")
   

2. Set the implicit wait to zero before using explicit waits:

   driver.implicitly_wait(0)
   

3. Prefer explicit waits throughout the test suite to avoid global side effects.
4. When a global implicit wait is unavoidable, keep it short (e.g., 1–2 seconds) and document its purpose.

What to Verify

To fine‑tune the recommendation, we need to know which WebDriver implementation and version you are using. Different drivers implement the polling loop differently, which can change the observed timeout behavior.