I know that the first presidency authorize the stake president to carry out this priesthood ordination by contacting a general authority (70) to carry out the ordinance Once you are baptized you are entitled to receive your priesthood and the restoration of your temple blessings ie endowment and sealed to your wife and children again
There is no time limit but the ordinance is carried out asap. The person is no longer under the the repentance stage as the baptism has taken place and is entitled to the ordinance as soon as a general authority is available
It all depends where you live in relation to the nearest 70 as to how long it takes. The church want to carry out this ordination asap because they want to encourage these people to go to the house of the Lord and feel of his love