As has been said above as long as the room temp is high enough then the livestock should be ok, nightime will be the problem though. I would advise to get another heater ASAP. You are in charge of the livestock you bought, so look after them to the best of your ability, they are at your mercy, they are totally reliant on you to provide them with the proper conditions for them to survive. Lastly but only as a temporary measure is to fill some plastic lemonade bottles with hot water and place them in the tank whilst you beg steal or borrow money to get a replacement heater. Sorry to sound so harsh but £15 - £20 for a replacement heater is really not that much taken into account the amount of money you have laid out so far on your setups.