You wont notice any difference if you inject and then immediately go workout, when compared to injecting and going and working out the next 2 days...as long as you are cycling properly which I hope I am not making a mistake in assuming.
As mentioned, the levels in your body should remain fairly constant if you are cycling properly and staying on a constant schedule.
I believe a good illustration of this can be found on one of the PCT calculator links ( i believe its in the Newbie Sticky) which will actually give you a graphical illustration of the levels in your system based upon the inputs that you provide i.e. what you are on, and what frequency and duration.
Hope that help'd