How to change 'nbf' value in jwt.io token

For some reason I want to change nbf payload value in my jwt token. I am trying to add value but unable to achieve it.

DateTime original = DateTime.Now;
original = original.AddMinutes(-10);
var seconds = original.Subtract(DateTime.MinValue).TotalSeconds;
var claimsIdentity = new ClaimsIdentity(new List<Claim>()
{
    new Claim("email",sresult.Properties["mail"][0].ToString()),
    new Claim("sub", accountName),
    new Claim("myv",seconds.ToString()),
    new Claim("nbf",seconds.ToString()),

Where I'm doing mistakes, nbf value not updated with my value. Actual nbf value is 1487049869(system generated datetime) but my value is 63622665869 (-10 minutes less than current datetime).

two things come to my mind:

you didn't show much of your code here, so I can't see how the token is generated, but if you have something like this:

var token = new JwtSecurityToken(_issuer, audienceId, data.Identity.Claims, issued.Value.UtcDateTime, expires.Value.UtcDateTime, signingKey);

then the fourth parameter is the desired nbf (not before). Actually you don't need to add a nbf claim manually, as it is one of the standard fields in a JWT

your timestamp seems odd to me

my value is 63622665869 (-10 minutes less than current datetime).

the timestamps in JWT are UNIX timestamps counting from 01.01.1970 00:00 UTC: https://tools.ietf.org/html/rfc7519#section-4.1.4 explains that a numeric date is used for the exp claim (and also for the nbf (not before) and iat (issued at) claims)

https://tools.ietf.org/html/rfc7519#section-2 defines the numeric date: