The idea that multi-tasking is the answer to squeezing more work into the same eight hours is actually creating habits that cause you to mismanage time. Granted, some people can juggle a phone call and typing a report at the same time.
Don’t be fooled into thinking that if you could just do three things at once instead of two, then you would better manage your time. Actually, you create more potential for making mistakes because your attention is divide in several ways. Nothing muddles time management worse than the time necessary to correct mistakes.