As a business owner there are so many things that become your job. My general rule of thumb for outsourcing in general is - delegate the parts of the business you hate doing, when the business has the means and extra revenue to do so. So when is it time to outsource marketing? When the business has spare revenue to pay for it and you don’t enjoy doing it.
I really recommend doing a DIY marketing strategy at first if you have the time, energy and inclination; then outsource it. The advantage to learning to do it yourself is that you’ll be able to talk the talk and have a better understanding of how it works. That way when you hire someone to take over, you can communicate and manage them better. Who knows, maybe you get lucky, you love it and are good at it.