There is no prob delaying ur rehydration time as this step meant for only protien taking..there are some jounals with 20 hrs time . It may depend on the strip length also
There will not be any problem if you increase the rehydration time. Improper rehydration will be a problem but, higher time will not. Generally 10-14 hr is recommended for rehydration. So, be sure about this and follow the same for all the set of experiments to achieve reproducibility. This time depends on the temperature and humidity of the room where this rehydration chamber located (to an extent) and depends on type of rehydration chamber (Open type or closed type) you use.
Are you applying any current during the rehydration step? If not, you can to run the rehydration step at a low voltage. This might improve the performance without any need to increase length of the rehydration step.