Why is there a message limitation for GPT 3.5?

Hello everyone, I am using GPT 3.5 but it suddenly popped up that I’ve reached the limit of messages per hour. I have several questions according to this.

  1. how does it work? is it 24 hours based or will GPT only not work at the next hour?
  2. what is the limit for GPT 3.5 per hour?