I usually fill and ice my cakes with Italian Meringue BC and then cover with fondant. I am looking for something to withstand the heat a bit more, so I have decided to fill with IMBC and ice the outside with Indydebi's BC. How do I let the icing set up before covering with fondant? Cover right away while cake is still sticky/tacky with icing or ice and refrigerate until solid then cover? I am just worried that once the BC 'crusts' the fondant wont stick.

Thank you!!

You can do it either way. If the icing crusts you can just spritz it very lightly with some water and that will help your fondant stick.

Due to the heat and humidity I always use a crusting bc (Indydebi's recipe).
After the final coat of icing I let my cake crust completely. When I'm ready to cover with fondant I place it in the freezer for 10-15 minutes (tip I learned from Sharon...sugarshack) then brush it with simple syrup using a pastry brush. I use this method for my ganache covered cakes as well. Planet Cake has a very helpful tutorial on youtube "how to cover a cake with fondant" that shows exactly how to apply fondant using this method.