I've recently had a few clients come record at the studio with no experience on how to approach mixing. Taking the time to record good tracks is extremely important, but mixing those tracks is also vital to the sound. Mixing is an art form that can take years to develop for an audio engineer. As a musician, you should respect the experience and creativity that your engineer puts into mixing your music. When you find an engineer that likes to think outside of the box, consider your music blessed that it will not have a canned sound and will benefit from the artistic vision of a passionate mind.
Taking the proper amount of time to mix is subjective based on the outcome the artist has in mind and would strive to achieve. A 10 minute mix can yield good results and a 10 hour mix can be remarkable. The time it takes to mix can depend on so many different factors and becomes virtually impossible to determine. Try to take momentary pauses in the mixing process to step back and analyze the current state of the mix. These moments of review give you bearing on where the mix is going and how far it still needs to go. The finish line is vague and it may not be apparent when crossed if you don't take a moment to pause and reflect.
Music is so unique and recording situations change constantly. There is no way to determine how long it will take to mix a song before it is completely recorded. The mics and gear used in recording fluctuate on various levels from session to session. The number of tracks to mix may vary based on what the producer has in mind for the final mix. Recreating the same mix from session to session is possible, but very rarely duplicated. It's the subtle changes that make each mix unique. The initial approach toward the mix is the foundation as to what direction the music will go.
Where do you start? Do you start with the drums and percussion? Do you start with the vocals and build the music around them? There is no right or wrong answer to these questions. The art is the creativity that you bring to the mixing desk. You can do the same approach every time and always get different results. The plugins and out board gear may change from mix to mix or you may use a template. There is no guarantee that the sound you have in mind at the start of mixing will be the sound at the end of mixing. This is a good thing because you will craft a different sound from song to song. If every recording had the same mix, the music of the world would not be as interesting as it is today.
Dedicating a fixed amount of time to a project has some detriment to the project. A mix is finished when it sounds finished. It could happen in 10 minutes or 10 days, but you have to let your ears be the judge of when a mix is complete. An unfinished mix will leave a bad taste in your mouth. Budget for enough time to finish a mix and then be pleasantly surprised when the work gets done early. Expecting quick results almost always leads to disappointment.
Allow the mix to be artful and you will be rewarded with satisfaction. The final mix is your legacy, so don't limit your mark on musical history with an unfinished mix. Legendary recordings were all mixed with passion and time. When you craft the mix just right, it will be played over and over until the end of time.