all I can offer is my personal experience with my first Brooks
I kept rides not too long, about 1 hr, maybe 1.5hrs--now, I should mention that the padded bike shorts I had at the time were just so so, the padding was not that thick, especially not compared to the nicer ones I have used for the last bunch of years.
So after an hour ride or so, my sit bones were always sore, but this makes sense as it does take time for the leather to take shape and start to have the dimples forming where your sit bones are. I do remember that it was a very humid summer at that time, so I was sweating a lot onto the seat, and this probably helped speed up the process. I put on proofide as recommended, but not too much, and that was it, just rode and rode.
it seems to me that about after 6 or 7 or 8 rides (ish) I realized that I wasnt being conscious of the seat anymore, and it just worked from then on.
but I am certain that it being very hot and sweaty helped it along. Perhaps if your padded bike shorts are better than the thin ones I had, it may be a bit better fro you for the break in period.
I second or third the emphasis on how important seat position is--ride with the allen key to make adjustments, and really listen to what your body is telling you, only you know what angle is good, I generally prefer level, with maybe a slight upward, but Im on dropbars.
proper "fore and aft" position is really important also, I recommend putting some tape on the rails or something as a reference-and again--be very observant and listen to your arse and dangly bits to make adjustments.
other than that, you just have to ride them.
You will find over time if you keep it, that very slight positional changes may be needed as the leather changes shape over time (down the road, in a while)
cover them if riding in rain, and always cover them overnight in case it rains overnight, a couple of plastic bags overnight for sure, and strong winds can whip off bags in a storm, so I put a plastic clip to keep them on.
for riding, I started using a plastic bag, and eventually got a fitted cover , which is nice.
re taking new on a trip--this is generally never a good idea, so I'd ride and ride and ride, and see how your nether regions are, its that simple. But if you only do short rides and then head off riding 4, 5 hours a day, you could be in an uncomfortable position, and that sucks, so only you can make this decision, strangers cant.