Can we make partial-day deductions from a PTO bank?

Q: If an exempt employee works for two hours one day, must we pay her for a full day, or can we require her to use her paid time off? What if she doesn’t come in at all for a day—must she still receive her full salary, or can we dock her pay for the day? We don’t allow employees to borrow PTO from the next year’s allotment.