Yes, writting an express backend is really simple, some plugins, error-handling etc. and you can run it in less than 1 hour.
But the Frontend with webpack needs definitely more time, hours and hours to fiddle webpack to your needs.
This project has a definded strucutre and support defined modules (react), so it could save you a lot of webpack config time, but you can not do everything with it. You have to use it as it is.
Setting up Webpack isn't even the time-consuming part, in my experience - it's getting the back-end and front-end to work together and having a comfortable development environment in which both live reload.
But the Frontend with webpack needs definitely more time, hours and hours to fiddle webpack to your needs. This project has a definded strucutre and support defined modules (react), so it could save you a lot of webpack config time, but you can not do everything with it. You have to use it as it is.