I guess it is a roguelike turn system but with very poor precision of 6 seconds. (the other roguelike I have played had 0.1 second precision).
So if your explanation is right (and I am reading the UI right):
At the start of the turn you get X “moves”. (100 by default, modified by various things).
During your turn you can do actions until the sum of “moves” used by the actions is 100 (or whatever ammount of moves you got). Then your turn ends. If the ammount of “moves” you performed was greater than the ammount of “moves” you had then the remaining is carried to the next turn.
The imprecision from such long turn duration allows exploiting fast actions pretty badly.
If you can do two actions in less than 100 moves then you are quaranteed to be able to perform them before any NPC can even move.So you can attack and step out of attack range.
And it is even worse. If the zombie takes lets say 120 moves to walk+attack then you have full 12 seconds time to dance around the zombie. (with more precise timing you would have only 7.2 seconds window to attack and retreat)
I guess shortening the turn duration would help with fixing the OP spears and the general “dance” around zombies to avod being hit.