How to know the time period server response in the Dio library?

You could use a stop watch to measure how much the request took

var stopWatch = Stopwatch();
    
stopWatch.start();
performReques();
stopWatch.stop();

// convert the duration to string
var elapsedString = stopWatch.elapsed.toString();

// or just get duration in seconds
var elapsedSeconds = stopWatch.elapsed.inSeconds;