How important it is to have a no surprise morning on the day of your GMAT?
Although the most important factor for you success on the GMAT is your preparation and studies, but the short term factors - like you health on the test day - is of equal importance, if not more.
I have appeared for GMAT 4 times (Oct'18 & Jan'19 -- Oct'19 & Dec'19) and my score on GMAT ranged from sub-650 to past-700.
I wanted my 3rd attempt to be the final one. Preparing on my own, I was able to crack the GMAT core after my 2nd attempt. I followed a strict study plan with detailed analysis of each questions, and I was able to reach a my personal goals on mock exams. But my test day everything changed.
On my exam day (3rd attempt Oct'19), I had a 12 noon slot (Banglaore, India). Filled with confidence, I left home with ample buffer. On my way I listened to music and gauged though my flashcards. I was planning my post exam activities.
To my surprise, when I reached the exam center, the security personnel informed me that the Person Center has be shifted. Rattled and stumped, I zoned out for a moment and this distorted my focus, ultimately leading to a disastrous score. Since the center was only 4 KM away and I had ample buffer, I was able to reach within time. But my mental state was too distorted, the panic mode continued till my first break destroying my verbal scores.
So couple of simple lessons from this experience :
1) Talk to you exam center a 1 day ahead of you exam.
Just call them and confirm your name is there, check the address and the parking details (Incase you are driving)
2) Check your travel route for road closure and traffic conditions.
The route to your center may not be familiar to you. It might be on a different side of the city where you do go often. So, it is always good to travel to your GMAT center once about 3-4 days before the exam. Also track the traffic on Google maps or any other app. Choose your ride to the center wisely, take someone with you to handle on road worries.
3) Practice meditation and self-calming methods
Trust me this is the most important thing to do. No one can control all the factors in life, you have to rather prepare to handle tough and uninvited situations.
Although these will not increase you score by any means, but it will ensure that the GMAT Score is the appropriate representation of your capabilities. It will ensure that your months of preparations and sacrifices are not undermined by some silly overlooked information or unlucky bad morning.Hope this helps. Good luck

for your GMAT.
PS :
Do participate in the polls.