"Picbasic Plus..." - I don't have that version.. I have PicBasic Pro. :-)

I've never seen a:

DEFINE OSC 3.2768

So I will tend to think that it is not supported as well.

But that's where having the external oscillator comes in on A.4

But at that point, personally I would probably go to a RTC if you absolutely need it to be so accurate.

If you did not need the accuracy, what I would do is simply keep comparing it with a known accurate source. And then say something like every time seconds gets to 40 or whatever it will take, add one tick to get it accurate.