Miles Booster

Can anyone tell me how long miles booster miles have taken to be credited to your account?
I am getting worried as I have reward seats on hold til weds and was told by FC on the phone the booster miles would take 24-36 hours but the T&Cs say 72 hours. I could buy the miles I need but I don't want to double up the cost if I don't have to.
I am getting worried as I have reward seats on hold til weds and was told by FC on the phone the booster miles would take 24-36 hours but the T&Cs say 72 hours. I could buy the miles I need but I don't want to double up the cost if I don't have to.