VoiceAttack actions are added using the GUI, except when importing from a .vap (which is not intended to be written or edited manually, but rather used to export existing commands from VoiceAttack by using a file to store the information).
The action you're describing does not exist, as pressing joystick buttons requires a plugin (and plugins are controlled using other methods, like their "Plugin Context" field).
However, if you had a similar action for a keypress, E.G.
Press A key and hold for 0,06 seconds and release
You add or edit a command, click the "Key Press" button next to the action list, press the "A" key on your keyboard to set that as the key to be pressed, select the "Press And Release Key(s)" option (if it isn't already), set the "Hold down for seconds." option to 0.060, then click "OK" to add the action to the command.
Most, though not all, actions can be replicated based on what is displayed in the action list in this way.