I personally would not do it. I guarantee you the cupcakes will look
much nicer if frosted the day of especially during these summer months when heat and humidity come into play. Don't know how many cupcakes you are planning to make but even if it's alot it really won't take you much time to do the day of, especially if you use a piping bag with a nice large tip. At catering gigs we transport large quantities of unfrosted cupcakes then frost at the venue. The frosting looks fresh, glossy and pristine that way, not dull, tired, droopy and cracked like some day old cupcakes can be.