The Honda Hornet CB250F, also known as the Honda CB300R in some markets, is a popular motorcycle known for its sporty design and performance. As for your height of 5'7" (170 cm), it is likely that you will be able to ride the Honda Hornet CB250F comfortably and place both of your feet flat on the ground when seated.
The seat height of the Honda Hornet CB250F/CB300R is approximately 800 mm (31.5 inches). While the exact length of your inseam and the thickness of the seat can affect how easily you can reach the ground, 5'7" is generally considered an average height, and many riders of your height have been comfortable riding motorcycles with similar seat heights.
This will give you a better understanding of how well you can reach the ground and if you feel stable while seated. Being able to comfortably plant both feet on the ground while stopped can enhance your confidence and control over the motorcycle.
Additionally, consider wearing appropriate riding gear and footwear with a thicker sole, which can provide you with a bit more reach and stability if needed.