Are you using the same recipe for flooding the cookies? If yes, then it doesn't take too long to dry...maybe an hour and you can put on your second colors. Use a fan on them if your really worried.
I use Antonia's icing to outline the cookies, but I add corn syrup to her recipe to flood them....it's a softer coat underneath. They're still stackable, but not too hard to eat. Kind of like a combination of Antonia's and Toba's glaze.
If you add the corn syrup, give them two hours to dry in between coats.
Are you using the same recipe for flooding the cookies? If yes, then it doesn't take too long to dry...maybe an hour and you can put on your second colors. Use a fan on them if your really worried.
I use Antonia's icing to outline the cookies, but I add corn syrup to her recipe to flood them....it's a softer coat underneath. They're still stackable, but not too hard to eat. Kind of like a combination of Antonia's and Toba's glaze.
If you add the corn syrup, give them two hours to dry in between coats.
Great tip with the corn syrup, I'll give that a try. My kids hate hard icing, but you can't stack buttercream 
I use Toba's, and I can add a second color almost immediately, depending on what I'm after. If it's adding accents or outlining, it's best to wait until the first icing has set or the second color will just sink into the first. If you want the second color to be on the same level as the first, I'd flood very quickly after the first. I've only had a bleeding problem once, and I don't think the time interval of adding the other colors played a part. I think the colors were just too intense. The only difference in the type of icing was that I used water instead of milk as the liquid.
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