try:
Event.observe(arrCheckintime[i], "click", function(){changeTip(arrCheckintime[i]); return false;}, false);
Event.observe(arrCheckintime[i], "click", function(){changeTip(arrCheckintime[i]); return false;}, false);
Event.observe(arrCheckintime[i], "click", changeTip.bindAsEventListener(this,arrCheckintime[i]), false);