Time it takes to mix a song

Mixing a song is a separate process and needs detailed attention and individual approach to every track even if working on the same album by the same artist. To get a good mix can take from about 4-5 hours for just vocals to 8-10 hours for a full mix of all the instruments and vocals. It is a mistake to think that mixing is only about getting the volumes right and slapping some compression/eq, there is a lot more to it. Editing audio, especially vocals correcting timing and sometimes pitch (especially when rappers sing themselves in the chorus without being trained in singing, if edited right still can get great sounding results and catchy choruses), effects processing and automation of everything from volumes to parameters on eqs, modulation, reverb, delay if needed, interesting effects on particular words and sounds takes time. It is worth to break the mixing time into a few sections and go and do something else to let the ears rest and reset. Also it is always best to leave the mix almost finished for the night, go to sleep and listen to it again in the morning fresh and tweak anything that needs it for the final mix then. You might wake up, listen to it again and hear nuances that escaped your attention after long hours in the studio the day before. Unless in urgency it is not advised to mix the song straight after recording if done by the same engineer, for many reasons it's best to leave mixing for the next day for fresh approach. There is no such thing as "15 minute final mix", within that time you can only take home from a studio a rough demo mix for reference, not a %100 final product at best it can possibly sound. From when I started engineering in 2007 to now the time I take to mix has only increased as I have learned to take a lot of details into account which is needed for professional mix.