I've always reasoned in terms of midnight because that's when the date changes. I use tomorrow to mean the next date and today to mean the current date. I'm not doing it for the sake of computers, that's just what I've always understood these words to mean.
I think using midnight as the anchor for the today/tomorrow distinction is a lot less confusing and ambiguous than having today/tomorrow not tied to the current date.
I think using midnight as the anchor for the today/tomorrow distinction is a lot less confusing and ambiguous than having today/tomorrow not tied to the current date.