If the elapsed time exceeds 24 hours, Sybase IQ returns sp_iqmpxincheartbeatinfo output like:
server_id,server_name,last_positive_hb, time_not_responding,time_until_timeout 2,'r2_mpx_cr_srv',Jan 14 2010 11:57AM,11:59PM,11:59PM 3,'w4_mpx_cr_srv',Jan 14 2010 11:57AM,11:59PM,11:59PM (2 rows affected) (return status = 0)
A value of 11:59PM in the time_not_responding and time_until_timeout columns means that the time has crossed the 24-hour limit.