Each spell has its fixed "until (duration)" condition or you say the condition when you cast it each time?
Well, Faerie Chains of the Familiar Slave says
So there is at least one canon example of the latter. That wouldn't prevent the former, so examples of the former wouldn't rule out the latter. Thus it seems to be the latter if so chosen.
The actual duration description,
, states "when the spell is cast," not "when the spell is created" nor similar. So the HoH:MC example seems to fit within this parameter properly.