Do you think it's possible that when Genesis chpt 1 uses the term "day", it means something other than 24hrs?

I know many people believe that the creative days in Genesis were each 24 hours long. However is there an example in the writings of Moses in which he uses the exact same word and it is clear that he meant "an indefinite period of time." This definition of "day" is often used in our modern vocabulary, but how long has it been used in this way?