Time preference is a comparison between the present and future. So the relevant factor is the time differential, rather than the value at any particular point in time. The relevant question is not "does a dollar bill represent at least $1 of utility?". The relevant question is "does a dollar bill have more utility today than tomorrow?" Eg. suppose we're in the midst of hyperinflation. Any savings I have are practically worthless today, and also are worth less tomorrow than if I'd spent it today.