Lives and keys that are sent to you are credited to your account
when your friends send them to you, not when you check the message.
However, an account cannot have more than five lives and three keys at any given time,
so if you are maxed out, lives and keys sent by your friends cannot be credited to your account.
In order to take full advantage of gifts, you should ask your friends to send you gifts when you are out of lives/keys.
If you repeatedly request lives&Keys from the same friend, you will not receive additional lives&Keys.
For example, if you request lives from friend A at 11 o'clock and then at 12 o'clock, the amount of lives will remain the same even if your friend accepts your request.