I am pretty sure you are wrong....  Though the time to finish  a building or research knowledge always increases as its level  gets higher, as you upgrade the Palace , EDIT: by then upgrading the oracle: END EDIT ,the research knowledge time is reduced from what it would have been if you hadn't improved the palace and  then oracle.

The game mechanics puts some restrictions on how you are allowed to progress,but getting the next palace level, unlocking the next oracle level and completing it  before researching more knowledge is beneficial.

I just came back to change my post..

What I was trying to say was, that by upgrading the palace you can upgrade the oracle, which means you can research knowledge faster.

Though I was never very good at proof reading my own writing and so often misread others, it is sensible to review everything that people write.

The first post talks about Town but the  response says Palace,and I didn't spot  that. 

You are right the first post is unclear as to what is being asked. 

Let me clarify my question again in case of confusing.

For example: My town is level 20. To upgrade knowledge "Troops attack I level 9", it cost me 7 weeks (some boost and equipment added).

Upgrade my town to level 21 can help me upgrade Oracle, which can give me 5% extra reduction time, it's clear. 

But I wonder when my Palace and Oracle are at level 21, the "Troops attack I" time is still at 7 weeks or will go up to 7 weeks 5 hours (hard to tell because the game hide this hour number, only day show up, and it's hard for me to check, too, unless somebody notice that at lower level) ? Then the Oracle & Palace upgrade are still costing me more than helping me. I experienced this kind of increasing in other game of Plarium.

No, I don't count on any bonus to cause the time effect. I hope that your answer is correct, but I have to test myself anyway and let you guys know (I upgrade the Offense lvl 9 first, calculate the how many boost I used, then upgrade town to level 21, recheck the Defense side and check if I need the same amount of boost to finish that upgrade).

Upgrading the town to level 21 and higher can help me to grow extremely faster than level 20. But there are pros and cons, haha, so I have to clarify.

It now seems that what you needed to ask was " how  much rounding in numbers is there, how accurate is the posted time?"

You already knew the answer, that up grading the palace and the oracle gives a reduction in research times,so why would you think that building to level 21 wouldnt, and actually increase it  ?

You are right about the pros and cons of going to Palace 21.

There are bonuses to be had, you can even try Jotunheim, but will probably find yourself in the  next higher league for competitions and though there is little difference to your abilities, will find that your targets are that much harder to reach, and the rewards less favourable.