It will make little difference if you wait longer as long as the baggie is air tight. Remember it is a hard environment for delicate resistive sensors so if it is a low priced digital unit shorter is better likely. Resistive sensors don't fair well in dirty, dusty and corrosive environments (urinate is bad for them too) The biggest problem with digital units they generally don't work well for long.

I do a salt test on all of mine 2 a year. Likely over kill but I hate not knowing.

http://www.omega.com/temperature/z/pdf/z103.pdf

might be of use too.