Doing homework while watching the television is multi-tasking, which splits the brain's focus and lowers efficiency. Furthermore, this means that you are concentrating on two separate things, more likely to get distracted to the TV than homework because it is more enjoyable. Thus, this results in you getting distracted and exceeding the amount of time it takes until you have finished your homework. The same goes for studying. You will not remember what you are studying as well because you are not concentrating solely on it.
Since watching TV while doing your homework slows you down, do them separately. Do some of your homework, and then you can reward yourself with a brief break in which you can watch a little TV. Then get back to doing your homework so that you can finish it and enjoy the rest of your evening.