With care, I have no doubt that a kayak could be built with 24" form spacing. However I am quite sure that the time you would save by having fewer forms would be eaten up by the extra time and care needed to ensure that the strips continued a smooth curve between the forms. Without that extra care, it would be very easy to finish up with a wavy curve instead of a smooth consistent curve.

I have often adjusted the spacing of the forms to suit the thickness of the strips and the shape of the kayak. My first couple I followed Nick's instructions and used 12" spacing with 1/4" strips. Since then I have abandoned the archaic US imperial measurements and used 300mm spacing with 5mm strips, 250mm spacing with 4mm strips on a child's 3.7 metre kayak and 250mm spacing with 3.5mm strips on a 5.2 metre K1. Thinner strips and tighter curves need closer spacing.

Unless you are prepared to risk humps and hollows, I don't believe you would actually save any time by using half the number of forms.