Help with finance

Hey hope someone can help me with how the finance works. I applied and got accepted. But it came up with 24 months with interest. I was hoping to use the 6 month interest free payment scheme. Is this something you can choose. Or is it applied to all finance options. So no matter what you get along as you pay within the 6 months it’s interest free?
Haven’t been able to get an answer for this.
Thanks
Jamie