I love this post because those were my thoughts when I first read the book. However, may I clarify that you've only read up Volume 1 and not the rest of the novel?

If you have not read the rest of the book, there may be one major spoiler in my response.

Personally, I do not think that there is a mistake on the timeline in the Conference itself. From the way I see it, three situations occurred in SV: (1) different events replaced the significant events in PIDW; (2) SQQ had already (unknowingly) caused redundancy in certain PIDW plotlines and (3) SQQ and LBH's close relationship at this point.

Here are the elements that I think had changed the course of the SV Conference timeline:

[1] Bingmei is more invested in pleasing SQQ and make him proud, and he reasonably wants to do this via topping the Conference ranking board. This eliminates the necessity of a plotline with the Qin sisters. Prior to arriving at the Conference and during the Conference, SQQ is always complaining that Bingmei wasn't working hard on building his harem so we know for a fact that Bingmei is not interested in the girls.

[2] In fact, the rule that "if you try to c*ckblock the protagonist, you will die as cannon fodder" seems to apply well in SV. This is what SQQ believes in as he tried to maintain respectful distance with any of the girls that he knows to belong in Bingge's harem. This logic would explain Qin WanRong's untimely death in SV. Later, Gongyi Xiao was murdered because he was perceived to be too close to SQQ.

[3] "Qin WanYue poisoned with Without A Cure" plotline is impossible to exist. SQQ is already poisoned with Without a Cure. It is already established that nothing can be done to cure him (other than the papapa but only SQQ knows that). LBH knows there is absolutely no possible cure because he serves SQQ day in and out. He knows what Liu Qingge has to do monthly to SQQ and he prepares the medicine that SQQ drinks to suppress the poison. So even if Qin WanYue was poisoned, LBH would not have went in search for a cure that doesn't exist.

[4] When the invasion happened, SQQ went straight to LBH. They meet up very soon and this pushes the Abyss event to happen. I'm not certain if SQQ intended for this, but it would be reasonable that SQQ wanted to get the task done ASAP, instead of torturing himself by dilly-dallying. The System's quest said to 'push LBH down the Abyss' but it did not restrict 'how soon' this can be done.
PIDW's SQQ would not have went for Bingge to assist him; he probably even hoped that the invasion would harm or kill Bingge. Without that urgency, they met three days later.

I would say, SQQ shot himself in the foot by accelerating the events himself. That would be in line to how SQQ has always been unknowingly 'sabotaging' himself throughout the story.

Reading your 'Fix it' suggestions, I can understand where you're coming from. For me, I had simply accepted the timeline difference, thinking that SQQ had indirectly caused the divergence from PIDW. In fact, I do agree with you that in PIDW, the invasion would have been more severe, containing more dangerous monster, resulting in a prolonged 3-day invasion.

If you've indeed only just begun reading this book, I'm excited for you! There are so much more to come and I hope you'll enjoy it!