Rather than relying on Acquisition:State which only tells you when the trigger has occurred, you should instead use one of the steps
referred to in the programmers manual in the section titled, "synchronization methods". Most commonly, the *OPC method is used. This does require
some setup of registers as documented in the referenced section, but once the OPC bit indicates a set state, this assures you that the acqisition has not just started, but is also complete. Your assumption that some time is required to process the measurements after the acquisition completes is correct, but the time required to do so is less than the time required to parse the incoming value query.