Well... This is an interesting topic. In Europe, as far as I know, the UK generally hasn't rounded off. But every country is different. I can tell you how it was in Belgium, because I do think it has experienced an interesting evolution with regards to recording times off birth.Let's just start with saying that there is no doubt that they now record the exact time of birth (according to the wall clocks mounted in the delivery rooms), my son has an exact time of birth of 22.41.
One generation back and things change. My brother's time of birth is registered as 5.20 am. Now with his Venus spot on the rising I can imagine that was pretty spot on, but that's not always the case. Also, they weren't very strict about it.
Another generation back and we witness something interesting: either my mother is born at 10 pm on the dot or times have been rounded off more. Yet, in my father's family, times seem to be rounded off very accurately (but still rounded off), my father was born 5 minutes before midnight Christmas, his youngest sister 45 minutes after midnight.
Then, the generation before that (my grandparents) have times rounded off to the hour.
The generation of my great-grandparents generally have the same, but the further down the family tree you go, the less accurate it seems to be. Generation 5 counting from myself, had times written down roughly "before sunrise", "at noon", "shortly before noon". The generation before that becomes "at night", "before noon", "in the afternoon" and the generation before that is mostly "time unknown" or "daytime" and "nighttime".
It just shows how little people used to care what time of day someone was born on exactly.
As for my time? It had to be rectified, the gyn who was supposed to deliver me didn't show up and the time was written down by him days later. In fact, my mother's description was probably more accurate that his, she said I was born about 3 or 4 hours after my brother on the hour
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