sendgrid SendAt doesn't work on Azure

Question

Ok, this is very strange!

I have a code that sends scheduled emails to people using sendgrid api (Sendgrid 8.0.5) . It works fine on my local system, but on Azure (on app services) it just ignores the SendAt time.

public async Task SendVotingTimeIsUpEmail(model)
    {
    sg = new SendGridAPIClient(SettingsHelper.Instance.EmailApiKey, "https://api.sendgrid.com");

    Email from = new Email(SettingsHelper.Instance.Sender);
    Email to = new Email(user.Email);
    Content content = new Content("text/html", "content");
    Mail mailSt = new Mail(from, "subject", to, content) { TemplateId = SettingsHelper.Instance.VotingTimeIsUpTemplateId };

    var datetimeOffset = new DateTimeOffset(model.ExpirationDate.Value, TimeSpan.Zero);
    mailSt.SendAt = datetimeOffset.ToUnixTimeSeconds();
    System.Diagnostics.Trace.TraceInformation($"Send at {mailSt.SendAt}");

    dynamic response = await sg.client.mail.send.post(requestBody: mailSt.Get());
}

I tried it 5 minutes ago. This is what I have in my log:

Send at 1480594002 (which is Thu, 01 Dec 2016 12:06:42 GMT)

And today is Nov. 30th, so I do not expect it to send the message now. But I just have received it in my email.

Any Idea?