I've tried sending you a message three times. Hope it worked this time.
Personally, I would prefer to refrigerate the cake. Since you have some time, why not make some more royal icing flowers as back up, then if the ones on the cake start to wilt or bleed, pop them off the cake and replace them with the new flowers right before you get ready to deliver.
I have been getting your messages and been replying, not sure why you aren't able to see them but thank you, that's a good back up plan! :)
I would hesitate to put RI in the fridge. Condensation will more than likely make it soft. Try putting just some flowers in not on the cake and leave them overnight, then see what they do when they come back up to room temp.
The RI flowers held up well, I first put a small sample in the fridge and then took it out to test it, I even sat the sample outside in the sun and it still held up, the colors did not run, the only thing I noticed was that the writing strarted to bleed very slightly but it looked like a small shadow effect. The icing I used for the writing was not RI and I did not use meringue powder in that icing. Thank you for all the advice!
Great news Wendy! Now you can do it without worrying