IMPO, you need to learn html, css, php

It takes just one working day if you are a perfect web-designer but it can take many days if you are new or untrained.

If you don't want to spend more time on designing and development you can also use ready made templates for your website else if you have patience and good grasping power you can use website builder and can build your website yourself. Having basic coding and designing knowledge will be helpful.

I always used to tell my kids "It takes as long as it takes." Wait... I still tell them that. In answer to the question it takes as long as it takes.

Seriously though, I understand your desire to compare yourself against other designers, but focus on your own skills and continue to refine your OWN timelines. Then you'll find that time consistently getting shorter and shorter. Never stop learning new things and you'll be all set.

You may use various template making tools and applications to do your work. You may customize your template within 2-3 hours of your own idea.

Tweaking templates also does require good knowledge, so I guess it will not be very difficult for you create a web from scratch. However, you require designing skills like Adobe Photoshop to create a good and eye-catching template.