the main thing is just to get your arse out there and ride regularly, not necessarily super long rides, but regularly, so you deal with and adjust stuff if necessary for the uni specific fit and comfort stuff (and or by simply riding regularly, your body does toughen up to a certain degree--this is not to say ever to ignore pain, misfit etc, hope you get my drift)
first of all, flying to europe just for a week trip and coming back is a bit tough jet lag wise, takes a few days min. and in my experience, usually a bit more, so you spend the bucks on a flight, and are just getting over the time diff and then you fly back.--sure, when I was in my 20s it didnt affect me as much, but there is still the money spent for such a short "travel" experience.
maybe do the trip and visit other stuff while over there (but another topic I know)
so, specifics on what days are hard--generally the 2nd and 3rd day are a bit harder, as you are more stiff, maybe lack of sleep catching up that the first day or so's adrenaline excitement cover up. So for me, after about 4 days or so you are getting more into it, body hopefully doing ok (if the bike fit and your fitness is good to begin with) and after a week, you really start to notice being stronger, and into the ryhthmn.
again, these are my personal experiences, but I reckon its more or less common for others, so a reasonable expectation for you as well.
Really though, the most important thing is to ride regularly, I mean why spend all that money to arrive there with little hours and kms of seat time, kind of a waste, plus you will enjoy the experience more as you wont be as bagged and will recover from jetlag and daily riding faster.
bottom line is to have fun, so prepare yourself properly and its a win win.
I commute regularly, so this helps the bum and leg muscles being in reasonable shape. It certainly does help doing longer rides so you are physically aware of how they are, plus it will show up issues with your shoes, your bike shorts, whatever, that it just makes sense to address or be aware of before youspend a few grand on a trip.
I know its a supported trip, but if there are options for shorter first days, do this, it makes a real difference. I figured this out even back in my 20s, ie doing 60km days for the first or so days, and it is nice to not overdo it when getting over jetlag and all that. Plus, you will be more rested for the following days, but again, its a supported trip so I dont knwo what flexibility there is, and only you know what distances you are comfortable with, and on a uni to boot.
this is like any activity, prepare properly and use common sense to do so, and it will work out.
Just get your arse out there and put in the miles beforehand, you'll have more fun on the trip if you do.