How long does it take for a startup business to be profitable?

This question is often asked by aspiring startup founders at various forums and hence I figured it warrants an answer on the forum. The time period to profitability depends on the business model, the setup/running cost & the vision that the CEO/founder has for the business. A services business will have a different unit economics than a products business. Similarly a B2B business has different economics than a B2C business. However, the most important is the vision of the founder. Being a foodtech guy I cant help but give a food example. Take for instance Restaurant A & Restaurant B. A is a single outlet QSR (quick service restaurant), no frills, no delivery,  while B is a delivery focussed multi-outlet, multi-city QSR. Assuming the food to be equally good for both, A could be made profitable within 1-2 years of set up. However, building a multi-city chain of QSRs would require a much larger investment and hence would become profitable at the company level in a much longer time. The thing to be noted here is that neither of A & B are good or bad. Its just the vision of the founder as to what he is happy building.