Thanks for the replies, many are very interesting. I knew the moments of sundown and sunset would be a factor to some, but I am very suprised to see many comments about it being a personal thing due to the time to wake up for work, etc.

In my mind, if one says "5 in the morning" they are primarily referring to the time being 5:00, with the 'morning' part being secondary and included to either differentiate between AM and PM or to specifically express something along the lines of "we got home so late it was already morning".

That being said, considering the time of 5:00 being the primary aspect of the sentence, and every person I have ever met shares my perception and agreement to the current time, I feel that the second part should include a more definitive definition of morning. Your morning may well start at 4:30 while mine starts at 10:00, however these 'mornings' are personal. When discussing something so definitive as time primarily, following up the time part with an indicator that is mainly personal, feels wrong to me.

Which bring me to my final thoughts or conclusion: we all have a different time at which we start our own personal morning, and morning does not have or need a definitive time in most contexts. However, considering a 'parameter' for 5:00 DOES exist, which is 'night', I still feel that when discussing 5:00 it should be followed up by this more definitive and commonly understood 'night'.