Calculating citizenship eligibility for PRs who live in Canada but work in the U.S.

One of the requirements for Canadian citizenship, is you have to have been physically present in Canada for three out of the last five years. But if you drive to the U.S. for work every day, does that count as a “full day”? If you are a Canadian permanent resident working in the U.S., your work days do not count against your physical presence requirement for Canadian citizenship as long as you have a residence in Canada and return for at least part of the day.