some problem with time prepositions....

[Unregistered]

Recently, I am confused about the usage of the following questions...

Is the sentence correct?
I had a date at 6:30 in the evening on May 15, 1999. ?????

1. on the weekend---mean a weekend, not every weekend?
on the weekends ----every weekend?
at the weekend ----only in British English?
on weekends---- no the ?
on weekend---- no s ?
at weekends

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2. why do we use "at night" rather " in the night"
Is the usage of " at evening" correct?
why do we add "in the " in front of evening?
in the evening
in the night
at night
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[RonBee]

I post mostly on the weekend. (Could be any weekend.)

~R