To-do lists cannot be measured in time. Most people use them to ensure that certain tasks are carried out, and these are crossed off as they are achieved. There is no measurement of time involved in a to-do list. In theory, if all we had was this there would be no way of ensuring a certain task was carried out on a certain day, because how would the days be predicted or measured without a calendar?
How could we arrange with another person when to meet and manage to get there are the same time? How would we plan our year. the to do list might take a week or a year and might be very different from other peoples lists whose actions corresponded to each other.