I'm not sure how much my opinion matters on the topic, given that I literally just started preparations - but I did notice the same thing in my first practice exam.

How far into your preparations are you?

I would imagine once an individual gets further into the habit of answering these types of questions every day it would be easier to avoid a slow start.

It's great that you noticed this phenomenon. The good news is that it's fairly common among test takers.
Perhaps any psychologist in the forum can come up with the reason for this, but I tried to go through a couple of super tough math problems before any mock test to get the engines revving! I wouldn't worry about actually solving the problems, rather just try to get the reasoning correct.

On test day, I went through a list of 5-6 questions from GMAT Prep that I had prepared specifically for this purpose...

Have had 3 month studying. I am retaking after bombing my first attempt (600) ---even lower than I had gotten on my very first GMAT prep (640 WITH NO STUDYING WHATSOEVER). Made two ciritcal errors in reptrospect.
1) A complete lack of time management which led me to guess from #20 onwards on my quant section---bought into this myht that the first few problems are critical and spent way too much time on them resulting in a lower than usual quant score--I am comfortably a 42-44 guy in quant but I produced a 36 when it mattered most:(
2) Not warming up. I felt sluggish out of the gate--stumped by a very easy probelm early on.

I dont really think I need that much further prep coz my quant foundation is solid enough for my tastes and ability. My strategy is to get a decent quant score (>43) and kill the verbal (>43) and hopefully that will result in 700+---Does it?I think the important thing for me is to just accept that I will get around 42/43 for quant no matter what and allow the GMAT Gods to do their work. i.e. just approach each question as if it were equally important and dont ignore the time contstraint. Be happy wiht my performance and excell at what I am really good at.(I rarely get comprehension and CR questions wrong) Any thoughts?

Time management was one of my biggest concerns too.
Why, just a few days ago, I was posting my time management problems in this very forum!
https://www.beatthegmat.com/impact-of-re ... tml#406039

For the time management issue, here's a simple trick that worked for me. I took up Ron's suggestion for this.
The first step towards killing the problem is to know that it exists!
There are 2 aspects to this. Time management per question (to keep it under 2 mins) and Overall time progression (whether you are staying on the dotted line as far as overall time position goes).

For the first issue, acknowledge that you have a problem. Think about it. If there's a crack in your floor where you tripped and fell yesterday, will you fall again today? I think you'll avoid walking on that side of the floor. Similarly, practice a 100 questions telling yourself that you will quit and make a reasonable guess after 2 minutes. This practice will hone your internal clock to shoot an alarm after 2 mins.

For the second issue, take 2 practice tests and refine your time progression.
Take up any timing chart that looks comfortable to you.
I went with the 10 minute timing chart. It suited me perfectly.

Hope this helps...