Question about sea trial

[vash]

My first question would be, how long does sea trial usually take? Although I have seen answers online saying "days", "weeks", but when I actually followed the development of some warships, their status often show "sea trial" for more than half a year and sometimes it is even longer before finally changed to "commissioned". It seems to be as long as "under construction" and "fitting out".

I thought sea trial is mainly for checking out if the ship is sea worthy, and to discover potential unnoticed problems. So why would it take so long for ships in "sea trial" to be "commissioned"?