create procedure lib_time_add_minute (
                     dattim timestamp,
                     minutes integer)
                   returns (
                     dattim_result timestamp)
  as
    declare variable days double precision;

    begin
      if (   (dattim is null)
          or (minutes is null))
        then
          dattim_result = null;
        else
          begin
            /* 1 unit timestamp = 1 day = 1440 minutes = 86400 seconds */
            days = cast( minutes as double precision) / cast( 1440 as double precision);
            dattim_result = dattim + days;
            /* or: dattim_result = dattim + ((minutes * 60) / 86400e0); */
          end

      suspend;
    end