the larger the capacity of the bottle and the more water you have in there, the slower the drop in temperature
most will drop around 2degC per hour for the 1st 12hrs from almost boiling with ambient temperatures around 20degC
the rate of temperature drop SLOWS as the temperature gets closer to ambient temperatures
at 24hrs after adding initial almost boiling water to capacity and only opening twice during the time for brief temperature measurements:
1.8L was 53degC (started at 83degC)
1L was 53deg C (although started at 93degC)
450mL was 43degC (started at 83degC)