If you are injecting subcutaneous you should be injecting more then one day per week with smaller doses.
If you are, it really doesn't make that much of a difference when you get tested as serum levels are pretty consistent for both Testosterone and E2.
Estrogen serum levels don't vary in concentration like Testosterone so it doesn't really make a difference when you get tested for E2 relative to your Testosterone injections.
However, E2 is usually tested along with a host of other panels, including Testosterone, so if you are injecting weekly you'd want to get tested the day before your next testosterone injection.