It depends mainly on your project and its functionalities. For a showcase site like dimario.ch, it can take a few weeks, to create the competitor of Facebook, it can take more than 5 years!
In our case, the longest project we have been given to develop took 3 years. We still take care of its maintenance and evolutions. As for the shortest, it lasted 4 weeks.
If time is a problem for you, we recommend that you start your project with a Design Sprint. According to an IBM study, starting a project with a Design Sprint can reduce up to 75% of the design and development time of a project.
To get an estimate of the development time of your project contact us, it's free and we will get back to you within a week.