Hi Dave,
Any Workflow run has two phases, namely planning and execution. Irrespective of Execute Immediately or Later, the planning always happens immediately, its only the execution of the planned activity can be run either immediately or later.
So what you are seeing is the expected behavior. Pls wait for a some more time, once WFA 3.0 is released, you will have the ability to include reservation in custom commands as well.
This will solve your problem.
Regards
adai