If you have a created a raid.
You should be able to use the API to trigger "raid now"
Which is a button on the front end UI which allows the streamer to skip the 90 second.
BarryCarlyon shared this idea
With the Start a Raid endpoint ( https://dev.twitch.tv/docs/api/reference#start-a-raid), provide a query parameter that when supplied, true and a raid countdown has already been started, immediately trigger the raid as if the broadcaster/editor clicked "Raid now" on the webpage