On large swimming pools, it is not unusual to have joints that are left over a weekend or longer. The key is the means by which the joint is dealt with. As with any concrete joint, the surface needs to be clean and free of laitance or other contamination. This can be accomplished by cleaning the joint while it is green on the first day or by cleaning with waterblasting, sandblasting, or wire brushing after the surface has gotten hard. As long as the joint is clean, all gloss has been removed, and the joint is dampened the structure should not be impacted by the joint. Also, 27 cubic yards in 4 hours is not necessarily slow production. Depending upon the circumstances, I would think that 27 cy in 4 hours was quite productive.