get timestamp in seconds from datetime in c#

Use DateTimeOffset.ToUnixTimeSeconds method to get time stamp. It will returns the number of seconds that have elapsed since 1970-01-01T00:00:00Z.

To get the timestamp from a DateTime:

DateTime foo = DateTime.Now;
long unixTime = ((DateTimeOffset)foo).ToUnixTimeSeconds();

For more detail:

https://docs.microsoft.com/en-us/dotnet/api/system.datetimeoffset.tounixtimeseconds?view=net-6.0