If you want to regulate the publication of rows so that a row is always generated for every interval, even if no rows arrive during that interval, use the OUTPUT ALL EVERY option.
This forces Sybase to publish the last valid result from an OUTPUT EVERY clause even if no new rows have arrived since the last interval:
Notice that now there is a row at 07:15:15, even though there was no AAPL row during that interval. In addition, notice that with OUTPUT ALL EVERY, publication of the last valid row continues repeating every interval even if no new rows arrive.