Let me start with an observation: Let's say it's half past 12 and you're heading off to bed, I personally would say
Tomorrow I have to get up early for work
And as far as I know all my friends would too, but when I got into a discussion with a friend about this we looked up the definitions where tomorrow is
the day after today.
and today is
on or in the course of this present day.
and day is
a period of twenty-four hours as a unit of time, reckoned from one midnight to the next, corresponding to a rotation of the earth on its axis.
(all quotes taken from the google.com dictionary)
Although there are a couple of more options for day both on the google dictionary and a couple of other dictionaries I checked, none define the term in regards to sleep cycles. So, is this usage actually uncommon in English? Or is this simply a fault in the dictionaries I checked? Or am I misinterpreting the definitions?
And just to be clear, I would have expected tomorrow to be defined as something along the lines of
Tomorrow. The time after one wakes up, or — if one is not sleeping — after the time the majority of people are asleep (normally around 4–5 AM).
But as I am not an English native speaker I did want to check whether that usage really isn't correct in English speaking countries.