Good morning, all :)

I recently got into cake decorating, because my daughter finally decided she wanted me to do her birthday cake lol. I've learned a lot, so far, thanks to this site. Anyway, on to my situation and inevitable question.

My daughter has chosen a red velvet cake and a Sofia the First theme, decorated with fondant. I plan on using SMBC underneath the fondant and would like to use a whipped cream cheese filling. I know that a cake covered in SMBC needs to be taken out some time before serving, so that it's not like biting into a stick of butter. This is going to be a fairly small cake, a 6" round on top of an 8" round.

First, how much time does a cake this size need in order to come to a servable temperature? Would that time out of the fridge make my whipped cream cheese dangerous? I wouldn't bother with a refrigerated filling, but it is a red velvet cake and it seems to be a bit of a sin to leave the cream cheese out of it lol. Does anyone have any filling suggestions if I can't safely have the whipped cream cheese?

Thank you all, in advance, for your expertise :)