Rob,
I'm sure there are lots of things that would do the job, but someone was selling one of these Mumford Time Machines the other day and I did some research and it looks as though it would do what you need. And a great great deal more!! In fact the delay might be a clever thing for you to use to capture a moment after the beam is crossed.
Hope that helps at least a little.
http://www.bmumford.com/photo/camctlr.html
David.