I tend to link mine.
I start one on All Saints and form a chain up to the last one which finishes on Christmas Eve.
I also have an Easter one which must end with the Divine Mercy Novena the night before the Divine Mercy feast so the chain starts the night before Ash Wednesday.
You can say as many as you want.
I have done one over nine hours before and for days afterwards it was all I could think of.
Novena’s are good for self-discipline becuase you don’t put off today’s prayers if you are tired because you are in the middle of something that you do not wish to break.
Don’t forget you can say a Novena of Rosaries.
I always feel stronger spiritually when I am saying Novena’s so I like to look for a feast day or a Saint’s day to organise a Novena for because if I go too long without saying one it becomes so hard to start them again.