I think you will probably be ok as will your nem. You don't need to wait 24-48 hours for your water to mix but it is a good practice. What I do and a lot of others do also is to get your rodi
in a container (5g bucket, Rubbermaid bin, garbage bin or even an old aquarium) and run a powerhead and heater on it then just add salt and walk away. The powerhead does the mixing for you, no shaking heavy 5g buckets or hand stirring required. I'm a big fan of work smart not hard so if I can make life easier and have a pump do it for me then I'm all in. I work out of town so don't always have 2 days free to mix water so I generally start it in the morning and then do my water change after supper. As long as the salt in fully dissolved and the mix is at the desired temp then your good to go.