If this is the same buttercream you were asking about in the other post, it has eggwhites and butter in it, so I would wait til Tuesday to frost the cupcakes or frost em today and put em in the cooler. If you are using american style then they should be ok out on the counter.
Just remember if you are using the Italian Meringue BC then you have to serve them room temp. So give them some time to come to temp before you serve them.
You can make IMBC days ahead and freeze it, then thaw and rebeat till fluffy. Or it will keep in the fridge for several days, just bring to room temperature and then rebeat. But I do make mine the night before.
I don't mean to put down anyone's recipe but I do hope you will try the IMBC without Crisco, the extra shortening is really not needed and the extra butter may make it seem to buttery to you.
http://forum.cakecentral.com/cake_recipe-2426-Italian-Meringue-Buttercream--Shirleys-Method.html
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