I can't seem to gain any completion %

All actions associated with the achievement (registration in tournaments, creating something, solving puzzles, crafting actions, etc.) must be performed only after you click the start execution achievement button, unless otherwise specified in the description of the specific achievement.

I have solved numerous puzzles over past few days but still get no completion %. So again I ask what is meant by 1st, 2nd,or 3rd "according to the decision date".

If no one solved the puzzle before you, you will be 1. If one person solved - you will be the second. If two - the third. The speed of the solution does not matter.