Oracle 11.2.0.4 -- "sofar" increasing slowly in V$SESSION_LONGOPS
The TIME_REMAINING in V$SESSION_LONGOPS is much like the time remaining on downloads in Internet Explorer or file copies in Windows: It is a guess, massively subject to change, and often not a very good guess. I use SOFAR divided by TOTALWORK to measure progress. As long as SOFAR is moving forward at the expected speed, there is no problem. e.g.

select opname, sid, serial#, sofar, TOTALWORK,START_TIME,round(sofar*100/TOTALWORK,2) pct_complete, 
LAST_UPDATE_TIME , round(time_remaining/60) as "Minutes Remaining"
from v$session_longops 
where sofar &lt;&gt; totalwork and totalwork &gt; 0 
order by START_TIME;