They problem is that they need oxygen in the water. danios are active fish and use up the oxygen pretty fast. Water can only hold so much oxygen at a time, and water that is still does not recirculate air. the amount of water and the number of fish would determine how long they would survive If you had an air pump, that wouldn’t be an issue, if you stirred up the water every few hours , or took a cup of water and poured it into the tank to create bubbles, that would put oxygen back into the water. If you need to transport them, their are also capsels that you can add to the water that realease oxygen in to the water there are also battery operated air pumps to use in case of a power outage, etc…
They are rather delicate, but they will probably survive without filtering for that short amount of time, but of course not without air. If you are using a waterfall aerator/filter and only don’t have a filter, then that is fine unless the aerator is not running in which case you need to get an aerator you place in the bottom of the tank or they will suffocate.