Depending on your product's accessibility to Creators, your brief's requirements and the style of content you wish to receive, the time it takes to receive content submissions may vary. Some brands can see content roll in after 48 hours of publishing their campaign, whereas others can take a little longer (say, 1 - 2 weeks).
If some time has passed and you have not received any submissions, feel free to reach out to your Customer Success Manager who will happily help you alter and optimise your brief for success.