It must be refrigerated at all times. If your fridge is not big enough, you may keep in air-conditioning 18-22 degrees. The cake will last out of fridge anywhere between 2-4 hours depending on ambient temperature. Sometimes, even if the place is air-conditioned (e.g. sports hall/chalets), the circulation is not ideal and the room may not be cold enough for it to last very long out of fridge.