I would like to predict how long it will take to preheat my oven based on certain variables. My dependent variable will be time it takes for oven to preheat. For my independent variables, I have the temperature I wish to preheat the oven to, the ambient temperature in my home, and the time of day.

I have my data collected, however I am not sure how to quantify "time of day" as a value for the analysis. I played around with it, and for one analysis I used the value 1 for tests run between 8am and 12pm, value 2 for tests run between 12pm and 4pm, and value 3 for runs between 4pm and 8pm.

Can anyone tell me if this is a good way to use "time of day" as an effective variable when running a regression analysis?

Thank you much!