What's the service call TPS limitation for Dalle 3?

Hi, my service is calling Dalle 3 api to generate images, we call the API to generate 4 images concurrently(Since dalle 3 supports only 1 image 1 call, so we have 4 api calls concurrently), it takes about 50 seconds in total, so it looks like not calling concurrently, is there are any limitation to call the API concurrently?

I know there are limitations to generate images per minutes, but if there limitation for Request per second?