knowlton's answer is perfect. You also have wingspan - which is the distance from tip to tip across a birds wings. Life span - how long you life - and also how long you have before food goes bad. "Spanning" meaning starting from one place in time and ending (or currently reaching) another by a certain time or distance. The plains of Africa span for hundreds of miles. etc "From here to there" in time or distance.

span time = period of time Example - Chinese history spans over 4,000 years. Span is often used for longer amounts of time.

a span of time = a period of time You can modify it by saying "a LONG span of time" or "a SHORT span of time."