It's similar like a ecommerce site.
For instance, site ABC is selling clothes, it has cloth A, cloth B, cloth C to choose.
My site will be selling design service. All the service we sell, we can create at the backend. Like how ecommerce site can create their product, key in product name, product details and so on.
logo design has basic package, silver package, gold package.
Basic package takes time 72 hours.
Silver package takes time 48 hours.
Gold package takes time 72 hours.
Now, Mike (Example client name) want to purchase logo design, and he selects silver package, he clicks "order now", then makes payment, and fills up the 'information required' form for logo design, and immediately the time starts ticking against 48 hours, after one day, it means the clock should show 24 hours left.
An example site is logoworks