Going on vacation will always remove 24 hours from your vacation bank, if you have at least that much, regardless of how much you actually end up using. If you use less than 24 hours, the difference gets added to the games where you're on the move, up to the time control, with the exception of those in no vacation tournaments.
https://support.chess.com/en/articles/8583943-how-does-vacation-work-how-much-time-do-i-get
In my previous topic, I was struggling with (not getting) Vacation days.
After writing to Support, I received some of them, but then they reset back to 3 again after closing my account for my inactivity period and having it re-opened after it. 
Things have then been working fine (I was getting 1 new Vacation day every 14 days) after that, and I even managed to raise their total amount to 6. 
So, I was not really caring about it, but then I stopped getting them again, and I dropped all the way down to 0. 
However, yesterday I checked, and I somehow had 30 of them, which made me REALLY happy! 
I don't know how it happened and/or who granted them to me, but I would like to write my huge thanks regardless. 
I just hope that it was not a bug (yesterday I was also struggling with having a few features such as quotes, smileys and images disabled - supposedly due to some new update that bugged out? 
) and that they will be staying. 
That was the backstory, so feel free to skip it.
The issue I have is that putting myself on Vacation has been working 'differently' many times, and I still don't understand how to 'work with' it. 
Now that I have 30 Vacation days, I would not really want to (recklessly) 'waste' them, that's why I am writing this topic. 
I will give a few examples/scenarios below:
A) Two times, I took Vacation for about 22 hours and it took away 1 full Vacation day from me, but it added 2 hours to my games (meaning that the first game to move in was for example at 2 hours before taking Vacation, and after I put myself out of Vacation, its timer raised to 4 hours
).
B) But, one time I took Vacation for 10 hours, and it took away 1 full Vacation day from me, and no hours were added to my games.
I was wondering that Scenario B perhaps had to do with myself going out of Vacation 'wrongly' (I always do it via Settings where I put myself out of Vacation and then I save them), but with scenario A, I did it exactly like this the first time (and it worked), and then I put myself out of Vacation by making a move in a Vacation game the second time, and it worked as well.
So, I figured out that this had no impact. 
Also, the weird thing is, that I always had my Vacation at X days 13 hours, so some time in the past, I must have took my Vacation just for 11 hours, and it worked 'correctly' (meaning that it took just 11 hours away from me, and not a full day
), but with Scenario B, it would show myself at 3 days 3 hours (after beginning my Vacation at 3 days 13 hours), and, after putting myself out of Vacation and saving my Settings, it immediately switched to 2 days 13 hours. 
So, for some reason, I can't seem to take Vacation for fewer than 24 hours no matter what, which is quite bothering me, as I would really prefer just the actual hours to reduce, so that I would be able to take it for shorter spans (ideally between 6 - 12 hours, e.g. before going to sleep), but I quickly learned to not risk it.
I thought that the remaining hours (up to 24 hours) would at least get added to my Vacation games, but this happened very rarely - one time, I even put myself out of Vacation in just 5 minutes after accidentally using the 'Play' bar and moving in a Vacation game, and I lost a full vacation day because of it, same as when I sent someone a Daily challenge during my Vacation (as I did not know that it would void it)! 
Any ideas why it's 'acting' so randomly for me, and if it's possible to somehow get it to work 'properly'?
Thank you so much in advance for reading all this!