Почему токен работает после своей expiry time JWT?

var rtokenDescriptor = new SecurityTokenDescriptor
            {
                Subject = new ClaimsIdentity(new[]
                    {
                        new Claim(ClaimTypes.Name, username)
                    }),
                Expires = now.AddMinutes(Convert.ToInt32(120)),
                NotBefore=now,
                SigningCredentials = new SigningCredentials(new SymmetricSecurityKey(symmetricKey), SecurityAlgorithms.HmacSha256Signature)
            };

var validationParameters = new TokenValidationParameters()
                {
                    RequireExpirationTime = true,
                    ValidateIssuer = false,
                    ValidateAudience = false,
                    IssuerSigningKey = new SymmetricSecurityKey(symmetricKey)
                };