Dianne:  Leave the wax paper on top of the frames to hold the pattie in case
it dries out and crumbles. The bees will tear up the wax paper and carry it
out the front door; because bees are excellent "house-keepers".
Depending on the bee population, the amount of nectar flow, and time of year;
each pattie might only last 2-3 weeks in the late spring and summer, but 2-3
months in cold winter weather.
I don't know your location; but bees will eat grease patties almost 12 months
of the year in Miami or Tucson, but eat very little up near the Canadian
border.
However, to be effective they have to be present ALL 12 MONTHS!
                                                                                                George