Eliad is right about the commercial bread versus homemade: the homemade stuff will sprout mold faster. If you don't have time or desire to bake your own, try using the bread from the bakery at your grocery store. The commercial bread usually has some preservatives in it that slow down the mold growth. Also, if the bread is kept on the counter in a plastic bag the mold will grow faster. If you really want to speed it up, try adding an orange peel to the bag: most citrus has some mold spores on the outside. You don't see the mold because they spray the fruit with anti-mold solutions to keep the fruit fresh longer.