At the time of pre-order, no charge is made to your payment card or store credit balance.
Be sure to keep earning and redeeming your points for Microsoft gift cards to lower your out-of-pocket balance!
That is all. 
ADDENDUM:
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How would we have used rewards points? I had to use MS store credit.
I’m sorry. I should clarify. Any store credit that you are going to use hasn’t been charged yet, so you can continue to add to store credit through MS Rewards.
Edited for accuracy.
Oh? When I placed my order my store credited was drained immediately. My balance this morning shows the funds were taken.
…or am I misunderstanding and should stop speed reading on a work break?
Hmm. My store credit was never removed. I even added to it today. See attached.
My credit still shows a balance.
Interesting! My credit went from $1,000 to $450 (I also bought the protection plan) instantly. Still sitting there this morning at $450. I can’t add to that amount, though so maybe it’s a display hiccup while the back end still has my credit maxed at $1k.
Hmm. 
From what I have heard if you pre-order with 100% store credit it will be taken immediately. If you paid with a CC 100% or partial CC and partial SC both will be charged when the console ships (order goes through officially).
So when buying with SC/CC it works like: “Pay with whatever store credit you have first” and the remainder on credit card. If it is like this you can keep on adding to your store credit, it’ll just adjust the split between the store credit and the CC.
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This is very helpful. Will add to the OP.
I think that is how it works, I haven’t tested it.
Makes sense, and fits both our scenarios (I think).
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I redeemed my points in anticipation, then the MS store was so sluggish that I couldn’t use them on the X purchase.
So I went and bought AC Valhalla, Watchdogs Legion, Cyberpunk and Hitman Deluxe with them (had more than 300€). 
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