LM is correct. The "Waiting Action" was officially cut because of issues, but apparently we missed the reference.
However, a potentially good way of handling it would be as follows:
Waiting Action - a declaration of an action that is triggered by a specified event. The "Triggered Action" (TA) must be one that is able to be completed within a single round. Declaring a Waiting Action requires 10% activity. The TA cannot require more than 90% activity.
The character basically does nothing until and unless the trigger even occurs. The character will act outside of the normal initiative order for resolving the TA. The TA happens AFTER the trigger event, not simultaneously, nor before.
If the trigger event does not occur before the end of the round, the character may continue waiting for it. In this case, he may increase the percentage activity for the TA to 100%
If the character cancels a Waiting Action before it completes, his remaining activity percentage will be equal to either 80% (if the Waiting Action is canceled before the 50% breakpoint) or 40% (if canceled AFTER the 50% breakpoint.
That should handle things nicely...