Lol, a long time.
My first online company, I spent around 6 months working around a day job, maybe more, developing the website and trying to set up social media content, trying to source products etc. I was constantly finding faults which needed fixing, better content for social media, better design for website, etc, rather than trying to get sales. I tried a few more times, before eventually getting a few people to help and just paying for the little things.
Imagine you are your customer, and what they will go through to buy from you.
Come up with a step by step plan your customer will take.
Then write down everything you will need to do at each step. Then put an estimated time frame it will take you to implement each action at each step. You'll soon see how much of your time you are using up.