When you go to bed!!! And plan on getting up once (at least!!) during the night, say at around 3 am if you turn in around 10.30pm, to be taken outside. It's unlikely that he'll be able to hold throughout the night at this age. I also recommend you have him in a crate, and have it alongside your bed so you can reassure him that he's not been abandoned. You may find yourself having to get up slightly earlier than normal too, but that shouldn't last.