day and date changing

Here in my region it is Thursday. At the time of writing, the time is 09:30 a.m. and the date is May 10, 2018. At 12:00 a.m. at night the date will change and it will be May 11, 2018.

My question is, will the day also change? Will it be Friday after 12:00 a.m. [here in my region] (when the date is May 11, 2018) or will Friday fall with the sunrise (here) that is around 05:30 a.m.?

In short, does the day change with date at 12:00 a.m. or it changes with the sunrise? If it changes with date now question is, at 12:00 a.m when we have May 11 here, will that be 'Friday night' or 'Thursday night'? If it turns 'Friday night' then question is, does a night come twice? Since on May 11 after sunset it will be Friday evening & night here in this region...

• How does this work in your own native language? Why do you think it works any differently in English? May 10, 2018 at 5:20
• Actually why I'm confused is that if I say, "We'll meet on Saturday night." does this mean before 12 a.m. or after? Because after 12:00 a.m. it will be Sunday if day changes with date. May 10, 2018 at 5:31

Yes the day changes at midnight.

If you say "We'll meet on Saturday night" It suggests meeting before midnight. If you expect to meet at 1am you would say "We'll meet in the very early morning of Sunday"

However, In casual use, "Saturday night" is from sunset on Saturday to sunrise on Sunday.

I went out on Saturday night and didn't get home until 2 am on Sunday morning.

I couldn't sleep at all on Wednesday night because I was worrying about my interview on Thursday.

The train travels overnight on Satuday, so can you meet me at the station at 3am on Sunday?

So it dark both at the start and end of Saturday, but "Saturday night" includes part of Sunday morning.