[NumLock]

Код:

uses
  DateUtils,
...
var
  currentTime, eventTime: TDateTime;
begin
  currentTime:=Now;
  eventTime:=currentTime+1;
  Edit1.Text:=IntToStr(SecondsBetween(currentTime, eventTime));
//  SecondsBetween
//  MinutesBetween()
//  HoursBetween()
end;