Get a better USB drive, it takes max of 1 hour, usually about 50 minutes.
You can’t install more than i believe 10 items in one section, you can’t install more than a percentage of storage available at once either.
Not going to happen, way more technical than you first think, Syn3 Updater is very automated, incorporating specific cuts at certain points keeping filesizes to a fixed amount is not a simple task, it was tried and abandoned, syn3 updater recommends using Reformat anyway, only reason not to is if you are MY20, more and more maps are ESN locked though so this makes its even more pointless to implement.
EDIT: to clarify, You can only install 10 items in 1 section, so it’s not possible to have it all in 1 go, this is why i was split in to 2, 2 is now too large for most regions also so it was split in to 3. 3 is what Syn3 Updater tries to use but it doesn’t get it perfect as it’s automated, making additional options to change when the delay happen is too technical, we have nested for loops in side other loops currently, its a disaster but it’s kinda the best way we can do it.
Reformat is 100% the recommend way unless you are MY20, it’s cleaner, simpler and quicker. EU takes less than 1 hour for sure, if it’s taking longer use a better USB drive, preferably a USB 3.0 drive (despite the car being usb 2.0, USB 3.0 drives need to meet requirements that USB 2.0 drives don’t so are usually faster even in USB 2.0 ports)