This expressions means; Those who wake up early in the morning will be more productive and therefore successful.

This proverb is based on the Latin phrase “aurora musis amica”
(aurora is the friend of the muses.) It is based on the old Norse idea
that Aurora – the personification of dawn – has gold in her hair and
in her mouth. In Norway it is said that pieces of gold fall out of Aurora’s mouth
when she speaks and from her hair when she combs through it.
And in Sweden, people think that a golden ring falls out of her
mouth when she laughs.The phrase means that those who wake
early in the morning are rich with time and opportunity.
Erasmus von Rotterdam, one of the most influential scholars of the
northern Renaissance, wrote the phrase ‘Dawn is a friend of the
muses’ to encourage his students in Holland, advising that the best
work one can do is often in the earliest hours of the day.