Typically there is an afternoon or evening torrential downpour that could last 15 min to an hour or more. You can get on with things the rest of the day. I would be careful of travelling out of Dili as roads can get cut due to landslides. You don't want to be travelling outside Dili from around 3pm onwards Dili due to the downpours but I'm a cautious person - some do it. Some of the main roads are not bitumen-ed and you slip slide around in and out of the large pot holes and too close to the hillside for my liking.