Time keeping / Date variation

[superlollo]

Hi everyone,

I bought a brand new sub c by an AD about 10 days ago and I noticed something pretty strange.

Of course as soon as I got it i set it to the correct time by synchronizing it to an atomic clock. After 24 hours i checked to see how many seconds it had gained/lost and it turned out that it was 3 seconds fast. I thought it was cool because it's well within COSC standards.
I checked again the next day, and the day after and it stopped gaining time: after 3 days it was still at +3 seconds....so it gained 3 seconds the first day, 0 the second day and 0 the third day.
I checked again on the 4th day (yeah, call me paranoid, hahah) and all of a sudden it had gained 4 more seconds, so I was at +7 total in 4 days.
Didn't check for a while and today I checked again and it's +8 seconds.
I'm really happy that the watch has gained only 8 seconds in 10 days (i think the accuracy is terrific) but I'm somewhat worried about the variance. Shouldn't it be gaining/losing the same amount every day?

Now, regarding the date, I noticed that it doesn't change at the same hour every night. Since I had the watch it happened to me to see the date change 4 times...twice at 00:04 (different seconds but same minute), once at 00:02 and yesterday night at 00:05 and a bunch of seconds.
Again, is this normal? I know the date change almost never happens at midnight, but shouldn't it be happening at the same time every day?

I think my watch is fully wound, I gave it the 30 turns the first time and gave it 30 more after 5 days...I wear it about 16-18 hours a day so I don't think it should lose charge. I only take it off to sleep (6-8 hours depending on the day) and I leave it face down next to my bed.

thanks in advance to everyone who will be able to enlighten me! (and sorry if i'm sounding paranoid, i'm just curious)