Service firms compete using delivery time guarantees. A model was created to analyze how these guarantees affect competition. Firms aim to maximize profit by choosing the best price and time guarantee. In a market with similar firms, prices and time guarantees are similar to a monopoly. Different firms offer different services based on their characteristics. High capacity firms offer better time guarantees, while low-cost firms offer lower prices. As demand for quick service increases, firms focus less on price competition. This study shows how firms behave in price and time competition.