Dialog Box Displays When Activity Selected

My activities include a list of several commands to different components. Some of them need time to initialize/respond before the next command can be sent. This can be confusing to the user. I need to show the user a dialog box where I can input a short message. For example, when an activity is selected a box is displayed with the message “please wait” while delayed commands execute. The box should dismiss after a selected interval, or when the timed command delay is complete without user input.