Software Development Timeline – How long does it take you to develop features?

How long would it take to build a web-application that provides CRM, document management and customer portal features? I understand the description is vague but I have gone through detailed specs with many developers and have received a wide range of timelines to complete the exact same project.

Timelines range from 1 month – 6 months. How is there such a big variance? I am sure experience is a factor however many of the quotes were from teams of developers and some of the faster timelines were solo full-stack developers.

Does the timeline also depend on the stack being used?