Mixing bottles?

ac4mvp

With pumping, if I have 5oz bottles that I pump into, but only get 2oz from each side - is there any issue with combining them into one?  Issues being that there is a weird mixture of foremilk and hindmilk?  Is this ever an issue even if I didn't pump the bottles at the same time, but mix them anyway? 

Also, with pumping is there an issue with giving a bottle of milk in the middle of the day if I pumped it the night before?  Isn't there something about milk production being specific to the time of day for a baby's needs?