I raise and distribute about 2500 queen cells per year. The cells are
raised in JZ BZ plastic cups and ripe cells are inserted into JZ BZ top
bar cell protectors. The cells and protectors are centered between frames
in the top brood box below the first honey super. No queen excluders are
used. The cells are inserted about the peak of our major honey flow in
July, often when pulling honey.

My experience indicates that an insignificant number cells fail to hatch,
that about 15 percent of the old queens will survive and about 20 percent
of the initial virgin queens that kill the old queen will not succeed.
About half of those hives will have raised their own queen.

Research has been done indicating a success rate of about 30 percent, but
many factors are involved. I have experienced a range of rates from 40
percent to above 80 percent. Also, some varieties of bees  consistently
yield lower rates(25 percent) than others(80 percent).

Best Wishes
D. Murrell