All were ejected successfully over 10 minutes period ( about 16.5 minutes to 26.5 minutes ) from takeoff. This graphic shows the ejection sequence w.r.t. Time and Height at which the Satellite was ejected. Table on right lists the satellites and when they were released. Green triangle indicates 4th stage cutoff. 3 Blue triangles show 6 satellites which were released in the bunches of 2.
Before we proceed further a small explanation about the process of release of satellites:
1. The sat is NOT 'thrown' in the required orbit.
The launcher carrying satellite is brought to the required orbit and engine is shut off .. it is now in the orbit around body moving under gravity of main body just like the satellite would be. Then the satellite is released and launcher is moved out of its collision path.
So under normal launch the last PSLV component also would be with the sat bunch even after 1 or 2 days.
Naturally the PSLV component also would be with the sat bunch after 12 hours.
But in this particular launch ( PSLV C34 ) the launcher is far away and in a different orbit ( slightly lower .. about 460 kms ) as compared to about 520 kms as shown in the figure here.
( Overall view is in Left and zoomed views ( From top and side ) are on right. )
Now coming to the question: Why did ISRO tried this experiment?
The 4th stage was burning for 8+ minutes before it ejected the satellites so it would heat the nozzels . After its shuoff the surrounding chill would cool the engine. This heating and cooling cycle could cause some changes in the characteristics of engine which ISRO may be interested to know before they take up a real multi orbit injection of satellites.
.Good wishes to you ISRO.