That is correct. You have to have shares at the end of the day to get the split.
It is like saying, "We are giving out free pizzas at noon. If you are here at 11, it's too early. If you are here at 1, too late. Be here at noon."
You can buy ATNP shares at 3:59 PM on APR 5, and you will get the split.
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At close of business...April 5....all ATNP shares will multiply by 5.
To compensate, the PPS will divide by 5.
If you want to know how many shares you will have, multiply them by 5.