Your proposed project is incoherent but it appears that you might want to record temperatures at 20 second intervals for a day, from one sensor, and later from several. That looks like 28800 readings - to start with.
First up, do you have an EEPROM that can handle all that data? Even if you do, I submit you would find it easier to use an SD card.
Second, what sort of room is it that warrants temperature readings so frequent? And with a thermistor? I suspect the results will make for some very boring reading.