Butter cake creaming method
I have dealt with the same situation - very warm in the kitchen and the butter gets super soft, sometimes with a very slight bit of melting. This has never negatively affected the outcome of my cake. 

But, anytime you think it may be too warm in your kitchen, you can put a mixing bowl in the fridge or freezer and let it get cold while the butter softens. Then, when ready to start creaming the butter and sugar together, transfer the butter to the cold bowl. This ensures that the butter will not continue to get warmer during the creaming process.