Sorry, can´t tell you about East Timor.
But just a word of warning about Indonesia: I heard many stories, and even met a couple of bikers, who had big trouble getting their bikes temporarily imported. One of them even HAD the carnet, but still his bike had been stuck at Jakarta airport for weeks (where customs claimed he needs a recommendation letter from the United Nations
It could be possible, that the land border to West Timor is more relaxed about the paperwork (I really don´t know, cos I never went there). But it is officially a carnet country, and the point of entry, and who´s in charge there, is the sun shining, is it your lucky day, etc., seems to make a big difference, even though they probably should have the same rules at every border. Entering from Belawan (Medan), the carnet was definitely necessary, even the company who shipped the bike there insisted I must have it. I´ve heard of just 1 biker getting in from there without a carnet (in -06 or -07), but he did have to fight for a few days with the customs, and the bike had Thai plates (both are ASEAN countries, so this might have made a difference).