This works well for the current 30 minute market. At 5 minutes there are no non-battery plants, other than hydro, which can start up fast enough to provide power to the market.
True for cold start, but gas plants can ramp in the 5 minute window if they are already running. But the market conditions would have to such that it makes economic sense for them to be in that operating condition.
Right and it takes them five minutes to ramp down, and the price market window will be 5 minutes. Which means they will have to bet on the price being high the next windiw too. Which means higher prices sustained longer because gas units won't be quick enough any more.
If they're ramping as part of a system reliability service, then should be doing it under automatic generation control, not betting on the energy market, and they would have committed a certain amount of up and down regulation some hours in advance. The cost question is whether it makes sense for them to bid for that reliability service to begin with.
Which goes back to my argument that this is to a large extent about market design and not technology.