How to convert cooking times
There isn't a direct conversion, and certainly not one applicable across a multitude of dishes.  The toaster oven supples dry, radiant heat that starts from the outside in, and the microwave supplies "wet" heat that starts 1" inside the food.  The only case where the two devices are interchangeable is if you just want to warm up some leftovers.

For mochi specifically, you don't want to use the toaster oven at all.  If not using a microwave, you want to use a steamer, and steam it for around 20 minutes.  Your goal is to make the dough wet and pliable and not dry it out.