Is there a single word for a "unit of time"?

If I were to have a text box for someone to enter an integer and dropdown list from which my user would select day(s), hour(s), minute(s) or second(s), is there a single word that would describe what is selected in the dropdown list. The best I can think of is "time unit", but was hoping for a single word to describe an arbitrary unit of time.

Solution 1:

"Time unit" is correct here. "Duration" and similar terms refer to a slice of time (like two hours) not merely to the unit itself.

Of course you may be able to simply leave the box unmarked -- if someone sees "days" in a dropdown they'll know what it's there for.

Solution 2:

Period, interval, or duration?