changeInterval appears to update immediately for long delays

Thanks - I'll change the documentation. I vaguely remember changing it - the reasoning was that if you made a really long interval, it got difficult to change it to anything shorter.

If you want the old behaviour it's easy enough to fake:

var interval = setInterval( function() {
  if (newInterval) {
    changeInterval(interval, newInterval);
    newInterval =  undefined;
  }
  // ...
, 1000 );
var newInterval = 1000;