If you want Siri to pause longer to hear your prompt before responding, you can change that in Settings > Accessibility > Scroll down to Siri > Change Siri Pause Time to Longer or Longest. See what suits you.
If you want Siri to display the response longer, that is something that is yet to be a feature. Apple welcomes your feedback via the link below. They review each and every feedback, and if enough people submit thoughts about the same issue, they may release it in a future update. I’ll say this is a feature I’ve seen many users want by posting here in the Community.
Feedback - iPhone - Apple