This depends on your specific business requirements, the complexity of your finances and comfort with bookkeeping tasks.
It also depends on how you want to spend your time – using your skills working for your business and yourself, or on your business. You need to compare and cost in your time spent on doing your own books to the cost of hiring a professional. We work on a fixed fee or fixed hours per week for your business as needed. If you are losing 20% of your time working for your business instead of on your business (one day per week) then this is usually an indicator that it is time to develop a finance team for your business so you can do what you do best!