How to add apostrophes to these sentences?

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by shumin001 at August 25, 2011

1. In three weeks time we'll have to begin school again. (An apostrophe between "weeks" and "time"? Why?) 2.We claimed the picnic table was ours, but the Smiths children looked so disappointed that we found another spot. (An apostrophe between "Smith" and "s"? Why?)