Hi,
I'm assuming that you're working on the project described here:
https://www.sciencebuddies.org/science- ... er#summary
In this project you use a calorimeter with an electric heater to measure the specific heat of water or other liquids like vegetable oil. Equation 3 in the project background section shows how electrical energy (current, voltage and time) applied to the heater is related to specific heat, mass and temperature change.
If you kept the mass of water and oil, the temperature change, and the voltage and current the same in both of your experiments, then time required to heat the liquids would differ due to the specific heats of water and oil. Vegetable oil has a lower specific heat than water so less time is required to heat the oil to the same temperature change.
Were your experimental conditions the same for your water and oil measurements? One explanation for your similar heating times might be lower current or voltage, or a larger temperature change in the oil experiment.
I hope this helps. Please post again if you have more questions.
A. Norman