This all depends on the amount of customization you're looking for on your store.
If you have the assets and all the content ready then using a Theme and building the structure could be as fast as a week. Let us know if you require assistance on that front, we'd be happy to guide you or do it for you should the need arise.
Thank you so much for your reply. I hired "Hubako Media" to set up the store on 18th of Jan. During which, I tried to make some changes on Themes, then they said due to that changes it will take more time to fix as per them although they originally said 10 days is the completion period. However, I still can not run my store. I don't know what actually take that much time. I actually want to start a dropshipping store. Coming 18th Feb, it will be 1 months setting up the store. I am not sure they will be able to complete setting up. I have already paid for the service. Since I don't really have idea about web design, I would like to hire another one who can complete the work and make my store to start to sell things as soon as possible, but I am confuse now whether I should wait for them to complete or should hire another one.