Difficult to say at this time of the year to be honest. Could you not contact your client early morning, ask if it looks dry? as in not raining etc other then over night dew dampness etc, then if the answer is good, set off and re-sand.
I think you are in the south-east London area? next week is supposed to be dry but cold, so if you have done or doing the work next week you might have a chance of getting it finished.