You can submit as many requests as you need. Your designer will work on them in order of arrival unless you've set a higher priority to a specific design request.
If you need an urgent request to jump up your design queue, just let your design team know or change the priority to "Urgent" and the team will pause whatever they're working on for you and start working on that task before moving to the others. It's all about the relationship between your designer and yourself. You can view all requests in the dashboard so you can prioritize them as you wish.