If you are contemplating doing this in one hit, then it's going to take a while.
From what I can see, the guidance is having the smoker running between 110-120C, and aiming for the meat to reach 95C.
I would take the meat out of the fridge a good six to eight hours before you cook, to allow it to reach ambient temp, this will save the smoker struggling to bring it up, and save you time cooking.
This is going to take you around one and a half hours per pound, 5kg is roughly 11 pounds so there's 16.5 hours.
If you are using charcoal, have plenty spare and a chimney starter, so any refuelling is painless and quick. If gas, have plenty in.
I would aim for 20 hours, just to give you a bit of leeway if you get problems. If the meat hits temp early, foil it well and wrap it in old towels and put it in a cool box, ( Just for insulation to keep it warm) this will keep it until ready. There's nothing worse than having a flock of hungry guests, and telling them it's going to be a bit longer. (Been there!)
Iam no expert here, and there may be better advice on it's way. The main thing is don't struggle, and try and enjoy the experience.
Don't forget to write down every thing you do, if it works, then you can go back and repeat it, if it don't you can backtrack and see where things could do with changing. If you make changes to the air flow, leave it at least half an hour before changing things again.
Have a read of this as well it may save you some pain.
I hope it all turns out awesome.