Continuity is an important element of writing.
If you are freelancing or writing for someone else, you need to find a way to attain continuity and flow in your work.
Being able to write only a few hours a month for a client can cause serious issues with your continuity, so be creative when finding ways to make it happen. You could try adding an additional hour or so to re-read your previous work before starting to write again. This will place you back in context before you continue.
Of course, the worst thing you can do is edit as you go. Write first, edit later and then write again.
Try to keep the flow in all your work and have fun as you see it unfold into a work of art!