Help with yeast agar culture growth measurement/data collection

Hello! I'm a current AP Research experiment, and my study is on the effects of sudden heat shock at different temperatures on Saccharomyces cerevisiae yeast culture growth. I'm using agar plates in order to grow my cultures, and I was wondering how I would determine the number of cells present. I know that the general answer would be to use a hemocytometer, but I don't think I have one within my access. I've seen some people suggesting the use of online cell counting programs, such as cellprofiler (link below). Does anyone know how valid this would be? If not, what other methods could I be able to use? Also, how would I incorporate my data into simpler numbers? Aka, what equations could I use to quantify rate of yeast growth and temperature change? Thank you so much! 

https://cellprofiler.org/