James,
Do you really need millisecond precision reaction times for this (the
pages that you link to imply that you do not)? If not, then I think
that E-Prime makes a poor choice for this task. If it were me, I
would just do this in html & CSS, and run it for free on any web
browser. That's my advice, helpful or not.
-----
David McFarlane
Twitter: @EPrimeMaster (
https://twitter.com/EPrimeMaster)