The time required to make an Ō-katana, also known as a great katana or a large-sized katana, can vary depending on several factors, including the expertise and experience of the swordsmith, the complexity of the design, the materials used, and the desired level of craftsmanship.

Crafting a high-quality Ō-katana is a labor-intensive and meticulous process that involves multiple stages, such as smelting the steel, shaping the blade, heat treating, polishing, and hilt and scabbard construction. Each stage requires time and attention to detail.

On average, the creation of a custom-made Ō-katana can take several weeks to several months, or even longer, depending on the intricacy of the design and the availability of the swordsmith. It is a time-consuming endeavor that requires a combination of traditional techniques, handcrafting skills, and artistic vision.

It's important to note that the time required to make a sword can also vary depending on the individual swordsmith's work process and workload. Some swordsmiths may take more time to ensure the highest level of craftsmanship, while others may have a more efficient production process.

When commissioning a custom Ō-katana, it's advisable to consult with the swordsmith directly to get an estimate of the expected timeline for completion based on their specific circumstances and workload.