Turn it back on once you have completed the contact arc you are trying to complete.
If you already have another contact with an arc you want to complete, check what level they are before turning it back on, and you will know when you will have to turn it back on again if you want to finish that contacts arc.
I do get to the point on my Origin Arc character that I need to level up a level or two before I can get a new Origin contact and/or get missions from that contact.
As I'm trying to avoid getting additional contacts, I do this extra non-origin leveling through police scanner missions. I'm assuming that there is an equivalent to the police scanner/newspaper missions on the Praetorian side, but I can't give you information on that as I have a great distaste for the early level Praetorian content and, therefore, I don't make Praetorian characters.