In a 2-person cockpit, it likely takes longer to FIND the checklist than to "check" or DO it! In the case of an RTO, the checklist will not likely be at hand, so it will take longer than an inflight fire.
Dehavillanddriver has a good point -- What happens if the FO gets on the PA and yells "Evacuate" before the engines are shut down? If the FA also fails (or is unable) to check the engine, [s]he might open the front door, only to have the slides sucked into the engine.
Might a few seconds make a difference? Absolutely! However, we must take into consideration that rushing may have adverse consequences, and the risk is greater than a few seconds' delay.