I would say a lifetime. It doesn´t seem very optimistic, but I think it´s true.
Then, each person has a very special combination of motivation, intelligences and interests that makes the teaching-learning experience unique and that makes it very difficult to define how long it will take for each person to improve a specific language skill.
As a general rule, to be able to speak more I would first increase the amount and quality of input on the target language; read more books, magazines and websites; listen to songs, watch films and look for opportunities of engaging in conversation with natives or other learners.
Hope this helps and never give up...