Returns a new DateTime that adds the specified number of years, days, minutes, months, seconds to the value of this instance.
Example:
DateTime AgendaValidTill = DateTime.Now.AddYears(10);
// add days
AgendaValidTill = DateTime.Now.AddDays(10);// add days
AgendaValidTill = DateTime.Now.AddMinutes(10);
AgendaValidTill = DateTime.Now.AddMonths(10);
AgendaValidTill = DateTime.Now.AddSeconds(10);