I have a ~400 sq. ft. area on which I laid 16 inch tile. I finish it
over the weekend. I would like to get started on the grouting today
after work, but I'm not sure if I can get it all done in the time I
have. Is there any problem strength-wise with doing what I can tonight
and then finishing up tomorrow? I know that the bag of grout I use
today may be a shade different from the one tomorrow, but with the bend
in the rooms and the furniture, I don't think that will be all that
obvious.

On a related note, there is one hair line crack that showed up in the
excess mortar showing between the tiles as it dried. It is about 2
feet long and has grown since I first noticed it. It almost seems as
if the mortar shrunk... It is what it is I guess and I may have a
grout line that needs a well placed area rug :-), but I was wondering
if there is anything you can do this late in the game to help it? As
always, thanks for all your help.

it's not optimal but you can grout in batches, mix it all dry first to
prevent color differences between bags/boxes, then mix up a batch with
part of the dry.

i don't get it - why is there mortar between tiles ?