I don't know if I'm being blind....but I can't seem to find a countdown timer in TuxGuitar, as there is in Guitar Pro... is there one?
I don't think so, no.
If a countdown timer is what I think it is then what I do is tell it to play the song looped then start at the end of the song. Then it gives you a little time to get ready.
That's...a bit lame really, you'd have though it would have a countdown timer included...