As concrete performance depends on prevailing weather conditions, it is always advisable to check your weather forecast before ordering concrete for the following reasons:
Concrete should not be laid where the temperature could cause the concrete to freeze. British Standard recommends +3 degrees centigrade and rising for laying concrete. It is also your responsibility to protect the concrete from overnight frost and wind. You can do this by covering it with polythene or straw.
Always ensure the surface you lay the concrete on is damp to avoid the moisture being sucked out of the concrete which could causing cracking.