The Delay for a Period flow allows you to delay processing of the next node in the Journey until a specified time period has passed. See Fig 1 below for an example where the Entrant event is a contact being added to a database, upon which the Delay for a Period Flow node will delay for a period of two days before the Journey progresses to the Action, Send an Email.

Fig 1

To select the length of the delay and the time unit, click the Delay for a Period flow node once you have added it to the Journey work area. Doing so will bring up this popup ("Properties") on the right-hand side of the screen.

Clicking the "Period Count" input field below the "Delay for a Period" label will allow you to enter the number of time units you want to delay. Clicking the "Period Unit" input field will allow you select the time unit itself, such as hour, day, etc. (See Fig 2 below):  

Fig 2

Once you have finished with the action's setup, click the "Save Properties" button.