SriKumar'ji et al - simplify it. No need to bring PhD thesis here - we will leave that to ISRO
Think of the PS4 going "up" and while going "up" tossing out the nanosats. P+ and P- are directions in which they are tossed off (ejected off using springs., nanosats are just 10x10x30 cm and do not have their own propulsion).
From the reference frame of S'hkota looking straight at the rocket - it is a straight line up and P+ and P- are vectors pointing at you and pointing away. Or visually - just turn this: +|- by 90" towards right.
Here is the ejection sequence:
1. PS4 Cut-off @16min 47.80 sec @alt: 509.536 km
2. 1st pair of nano sats separation @18min 32.80 sec @alt: 511.719 km
3 last pair of nano @28 min 42.80 sec @alt 524.075 km
Here is the brochure (AmberG flight profile details you are looking for are as well in that brochure): http://www.isro.gov.in/pslv-c37-cartosat-2-series-satellite/pslv-c37-brochure-0
AmberG., can you please do some research on "stage passivation" and "degenerate orbits"? This are standard engineering practices of space launches where theory does not come into picture.
For others., the final stage always has additional fuel. Also has charged batteries etc. Basically it has enough of energy that if not properly released may cause an explosion (remember PS4 has hypergolic fuel and over period of time the storage valves may leak causing the fuel to mix up and go boom). Uncontrolled explosion will lead to space debris. Yes., even batteries heat up and may explode - more likely in space than in your pockets like the phone batteries.
Hence the goal for all last stage boosters is to remove any stored energy., this venting out the energy (generally fuel and draining the batteries) is called stage passivation. While the stage is passivated., it may also put in a degenerate orbit. That is a highly elliptical orbit that causes the stage to eventually re-enter earth's atmosphere and burn up. This is better than keeping the stage orbiting around for several more years as space junk.
Of course the general practice is to passivate the last stage at the earliest opportunity and put it in a degenerate orbit which will lead to burn up and if there is any debris the fallout can be in pacific ocean. However, the last stage itself can be used to do additional studies. Or sometimes a stage itself is reused as in skylab.
Even the satellites are passivated and moved to a grave yard orbit. In case of GEO sats., the orbit of the satellite is boosted up by some 360 km and the sat is passivated (basically all stored energy is removed). Note that it is easier to boost it up rather than bring it down (energy required is less to boost it up, it is already flying high!)
Now what ISRO plans to do with C37 PS4 stage *may* be found in this recorded (it is not live any more) video: https://www.youtube.com/watch?v=yPtFNJ2SSUw
. And there are some further gems