Personally, I don't think your whip cream filling will last overnight with out being refrigerated. I would also think it would cause the cake to settle as the whip cream possibly melted. I found this recipe below here on cc and it says it requires refrigeration.
I am also aware of something called stabilized whipped cream. I googled for a recipe and found the recipe below which still states that it needs to be refrigerated. I am not aware of a whipped cream filling which does not need to be refrigerated. If it were me, I would either make the cake the day of the event or I'd be googling other mocha filling recipes.
That's about all of my two cents worth. I hope this helps.
WHIPPED CREAM STABILIZER
1 tsp. unflavored gelatin
1 c. heavy whipping cream, at least 24 hours old
4 tsp. cold water
1/4 c. powdered sugar
1/4 tsp. vanilla
Combine gelatin and water. Let stand until thick. Then place over low heat, stirring constantly, until gelatin dissolves, which takes about 3 minutes. Whip cream with 1/4 cup confectioners' sugar and 1/4 teaspoon vanilla, just until it is slightly thickened. While beating slowly, gradually add gelatin to whipped cream mixture. Whip at high speed until stiff. Cakes frosted with whipped cream should always be refrigerated.