For First Part of Question
From the perspective of the check issuer, there should be no journal entry to record the reduction in cash until the date listed on the check. From the perspective of the recipient, there should be no entry to record the increase in cash until the date listed on the check. Thus, the date on the check effectively postpones the underlying accounting transaction.
For Second Part of Question
"The Supreme Court held in Interstate Transit Lines, 319 U.S. 590 (1943), that a corporation could not deduct expenses that it paid on behalf of its wholly owned subsidiary. "(For detailed decision you can check this decision from Internet)
This Decision would be applicable only at the time of actually payment only,for Post dated Cheaques, answers is same as mentioned in first paragraph.