The process and the implementation time varies depending on whether you want to opt for Standard Implementation or Custom, Enterprise level implementation.
Standard Implementation uses pre-defined templates and making some modification, putting your logo, design and images, setup the shipping and payment methods that you use. Usually, it takes a 4-8 weeks for Standard Implementation.
Custom Implementation takes longer time mainly because the site is developed from scratch by the Professional Designers and Developers. It take anywhere from 1-6 months for a custom site implementation.