How long to QT new fish?

In an effort to maintain hope that my 10g tank will eventually cycle,
I'm planning what to do when it's done... And at present, the plan is
to get three neons (to keep company with the three that are in there
now (long story, I know now, don't listen to fish stores)).

My question is, how long do I keep the little guys in quarantine
(assuming there are no problems observed during the QT - I know if
there are problems observed, the QT time will have to be extended)?

Thanks,

Liz