If you immediately begin to remove the grout without trying some other remedies first then THAT'S MOVING TOO FAST.
I would mix white vinegar and warm water 50/50. Use a soft brush to scrub the white areas. Some of the liquid is likely to penetrate into the grout, that's a good thing to a point. Straight vinegar will also penetrate but linger longer and your house will be smelling like a salad for days.
The time lines don't mean that much and they aren't critical. If this had happened six weeks down the road from now you would still have the white grout to deal with.
Try this and if it doesn't work we'll do something else. I hate to see you have to remove that grout if it isn't completely necessary.