4 pips to weapons is not absolutely necessary, if you want to put a couple of pips to shields. When your energy diminishes in WEP, the guns just fire more slowly but can still kill the Sentinel. If you reload the SRV with upgraded ammunition instead, the killing is over very quickly.Good luck! I managed after much cursing (my fault) to get all module blueprints.
Here are my hints:
It is dark there, maybe there will be more light today (it is a 20 day period), but Night Vision helps a lot. I hope you have a ship with point defense, like the OP described. The PD should be on top of your ship, under your ship they won't help. I had 2 (DBX), and they worked well. Do not forget to set 4 pips to weapons before leaving your ship, and park it exactly like the OP describes. This works like a charm.
Next I recommend to drive around with your SRV, to get your bearings! This is very important, not doing it cost me my first two tries because of timeout. Visit every energy pillar (they are sunken, if the scenario has not started yet) except the first one. Do not drive on the X, stay far from it. Also you can farm the pillars with destructible panels. Expect up to 4 (normally 3) sentries to appear and attack. There is no time limit, and it is always just one, so you can train how to kill them! Also this has the advantage, that they later, during the timed run loading the energy pillars will no longer appear! You can also farm the Guardian Obelisks, they have a glowing side you can data scan, this will give you needed data materials. There are 6 pillars with destructible panels, which will give you 3 materials each.
After having found all 5 pillars except the first be sure you have your bearings and know where they are. Be sure how to drive to the pillars. Then go to the X, as OP describes and start the scenario. The sentries will spawn quite far away, as soon as you can target one of them, you must set 4 pips to weapons in your SRV, or it will take too long. If your point defenses work well, nothing bad will happen, worst case your SRV shield gives out. But the sentries are not very aggressive, if you drive into cover they mostly will not pursue and you can give 4 pips to system and wait for your shields. During the timed exercise there will be no time for this. But it is not hard, once you get the hang of it.
If your point defense does not work, or not work well, then you should always put on your handbrake on the SRV, otherwise the missiles will displace and maybe capsize you.
After charging the last pillar 4 sentries will appear. But they are distributed, so that they are fairly easy to dispatch. Also the timer ends and you have enough time to do this. Again, take your time, try to pick up materials the sentries drop. After this drive up to the X, don't forget to take a Guardian Relic, and do as in the OP described. Two more sentries spawn after scanning, but they are not hard. And now you have one blueprint more.
Also - should you have a timeout, the scenario will end. But you still can drive around and farm materials. In this case it says, the scenarios is 'reset'. Don't believe it! It's not true. The scenario is not reset, driving to the X will do nothing. You have to log out (as the OP describes).
Also - after the patch there seems to be a problem with skimmers, where the game crashes if you fight them. The problem could be at this site too, but for me it only lead to a client hang during logout. You must end the client with the task manager. But this only happens if you killed a sentry during the session. Without this it works normally.
Hope this helps - o7
Handbrake is important for both kinds of attack from the Sentinels. The direct fire from the Sentinels (as opposed to indirect rockets) push you backward and over if you don't have the handbrake applied. You can see the fire tipping my SRV in this image (well, sort of).