The rules regarding pre-flight checklists and engine status found on pages 71-72 in Strategic Operations are all in regard to the craft lifting off, but this question is about weapons readiness.
Here's an example: an Overlord dropship in cold engine status is sitting on the launch pad (let's assume for simplicity's sake that the entire crew is onboard, awake, and at their stations) when a surprise attack is initiated and enemy forces are on their way to the spaceport. What has to happen (e.g. does the preflight checklist have to be completed and/or does the engine status have to change from cold to either warm or hot) in order for the Overlord to be able to be used as a grounded weapons platform in the event that the attackers reach the spaceport before the dropship is able to lift off?