How to use timer object with Psychtoolbox ?

I have a visual stimulus developed in Psychtoolbox. I want to use timer to run an execution of a function (function that records EEG signal) after 2 seconds of the display of the visual stimulus. Is it possible to use the timer object ? I tried but I keep on getting this error:

" The name 'BioPotentialSignals' is not an accessible property for an instance of class 'timer objects'. "

Has anyone seen such problem before ? It would be great help if some suggestions are provided.