var initSeconds = new Date(2010, 0).getSeconds() //january 1 of 2010
, BASE_NUMBER = 5000000
;
setInterval(function() {
var curSeconds = new Date().getSeconds()
, elem = $('#mydisplayelem')
;
elem.text(BASE_NUMBER + curSeconds - initSeconds);
}, 1000);
Something along these lines... this won't do exactly what you want, you need a better time calculation, but this should get you started.
Also, see this article about calculating date diffs.