We played with the soap in the sensory bin for 2 days before it really crumbled a ton. I think that depends on how much your kids pull it apart and break it apart. After playing with it, I rinsed the soap off the water beads and we had no problem reusing them. The microwave does have a residual soap smell for a little bit, but it definitely went away quickly and didn’t linger longer than that day. I’m not sure about the wattage of the microwave, but you can always just keep it in there for shorter or longer to “grow” it to the size you want.