Is a delay between questions in a questionnaire reasonable?

I would like my users to answer several questions. They have come to my site with the intent to do this. https://www.typeform.com is a good example. Most of the questions are multiple choice.

Which is best: to switch between questions immediately (<10ms) or have a delay (e.g. 400ms) and fade between the questions (pages).

I can prefetch all possible questions that could follow the current one, so this is not a technical question. Is there any research on this?