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There will always be some variation in the amount of time it takes a program to do anything–on a typical computer there are tens to hundreds of processes simultaneously competing for resources, so the exact load time will vary depending on how much else is going on at that exact moment.
The best way to benchmark is not to look at the time take by a single page load, but rather the average time over a bunch of loads. There are many tools to help you do that–Apache jMeter is one.
You may also want to look into profiling your app rather than just measuring the overall load time–that will help you identify which bits of your code are called most frequently and contribute the most to the total time taken. Guess-and-check optimizations are likely to be much more time consuming. See the Django docs or Google “profiling django” many more resources.