The “Shifts” sidebar says that shifts are 6 hours long, but it then says the Sleep Shift is “the eight hours allotted to your rest.”
How long is a Klingon standard day? Is it 24 hours? if so, then three 8-hour shifts is probably best (and would be easiest for players to follow). Otherwise, you might need 4 (or more) shifts, and that doesn’t mesh perfectly with the first, second, and third officers each running their shift (with the captain running all whenever he feels like it).