I would hope that Fiverr is not a representative example of a typical employment process. I understand you have to show that you're not a laggard when it comes to communication, but being dismissed for not replying to a message in 5-10 minutes is insane.
I haven't hired on any platforms like Fiverr for a long time, but if someone replied in 5-10 mins, I would be likely to assume they were an agency masquerading as an individual, or someone that isn't very busy.