• I walked for/#in 20 minutes. 001

• I walked to_Goal the store in/within/#for 20 minutes. [see Interval#005] 002

• I walked a mile in/within/#for 20 minutes. 003

• I mowed the lawn for/in/within an hour. 004

Note that the presence of a goal #002 or extent of an event (a mile in #003) can affect the choice Duration preposition, blocking for. #004 shows a direct object which can be interpreted either as something against which partial progress is made—licensing for and the inference that some of the lawn was not reached—or as defining the complete scope of progress, licensing in/within and the inference that the lawn was covered in its entirety.

The object of a Duration preposition can also be a reference event or time period used as a yardstick for the extent of the main event:

• I walked for the entire race. [the entire time of the race] 005

• I walked throughout/through/well into the night. 006

• The deal was negotiated over (the course of) a year. 007

But over can also mark a time period that contains the main event and is larger than it. While the path preposition over highlights that the object of the preposition extends over a period of time, it does not require that the main event extend over a period of time:

• He arrived in town over the weekend. (Time↝Duration) 008

Note that during can be substituted for over in #008 but not #007.

Some for-Durations measure the length of the specified event’s result:

• John went to the store for an hour. [he spent an hour at the store, not an hour going there]¹ 009

• John left the party for an hour. [he spent an hour away from the party before returning] 010

A Duration may be a stretch of time in which a simple event is repeated iteratively or habitually:

• I lifted weights for an hour. [many individual lifting acts collectively lasting an hour] 011

• I walked to the store for a year. [over the course of a year, habitually went to the store by walking] 012

See further discussion at Interval.