Adding time period for analogue output

Hello,

I am trying to add some additonal functionality to the vi below to allow the user to output a voltage (DC) on ports A0 and A1 for a duration of there choosing. Somewhere along  lines of 0 to 30 seconds, then returning back to 0V on the output when the time period is complete.

I don't seem to be having much look in achieving this. Can anyone point me in the right direction?

Thanks in advance!