In my humble opinion,
Once you get the PER, and ur file is transferred, it sits there for somewhat 6 months, Then they add a line in ur ecas which states that they have started processing you application. ( this is where ur file is opened by the officer at VO) ( again my experience not necessarily will imply on u. )
In the 6 months gap even if you don't have the amount, it wont be a problem, ( Like I don't have mine now)
But once you are close to 6 months keep the money, so that if they ask you can show it to them.
Once again, it is my humble opinion, and this is what i have learnt and this is the same path I am gonna follow.
Others may differ and its their experience. ( their experiences and thoughts are more than welcome.)
So please do what suits you best