Which word indicates a time length or duration?

The word "since" indicates a time length or duration because it refers to a specific point in time when something began and implies the continuation of that action or situation up until the present. For example, when someone says they have lived in a certain place since 2010, it suggests that their residency started in 2010 and continues to the present moment. This usage conveys both the starting point and the ongoing nature of the time involved.

In contrast, the other words convey different meanings. "After" suggests a sequence in time, indicating an event occurring subsequent to another but does not denote an ongoing duration. "Always" denotes a constant state without specifying a beginning or duration. "Then" is used to indicate what happens next in a sequence, without reference to how long something lasts. This distinction emphasizes "since" as the word most clearly connected to a time length or duration.