There is a label 'Duration' on the graph display which indicates a time of 1:40, or in other words 100 seconds. This is how long it takes to complete one sweep of the graph.

A vertical grid line can be made to appear by right-clicking on the graph and selecting the option.

The update rate can be adjusted from the default of 1 sample per second, but cannot be made more frequent than this.

The maximum, minimum and average values of any counters that are displayed are based on the current sweep of 100 seconds. At least this appears to be the case from my own observations.