If I collect and put the stool in the fridge now and take it to the lab in…

If I collect and put the stool in the fridge now and take it to the lab in the morning, is that a problem? Or should I go straight in the morning? We don't go to the toilet according to schedule, but whenever we want. It's hard to guess if the lab will be working and I'll have someone to take it to get it done.