时间戳转换

https://stackoverflow.com/questions/249760/how-can-i-convert-a-unix-timestamp-to-datetime-and-vice-versa

• Unix time in seconds to UTC DateTimeOffset:

DateTimeOffset dateTimeOffset = DateTimeOffset.FromUnixTimeSeconds(1000);

• DateTimeOffset to Unix time in seconds:

long unixTimeStampInSeconds = dateTimeOffset.ToUnixTimeSeconds();

• Unix time in milliseconds to UTC DateTimeOffset:

DateTimeOffset dateTimeOffset = DateTimeOffset.FromUnixTimeMilliseconds(1000000);

• DateTimeOffset to Unix time in milliseconds:

long unixTimeStampInMilliseconds = dateTimeOffset.ToUnixTimeMilliseconds();

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Note: These methods convert to and from a UTC DateTimeOffset. To get a DateTime representation simply use the DateTimeOffset.UtcDateTime or DateTimeOffset.LocalDateTime properties:

DateTime dateTime = dateTimeOffset.UtcDateTime;