You can take as many trains per day as you please.

On mobile pass a day is measured from 00.01 to 23.59 CET, any train you start travelling on within that is counted for that day. A train can continue past midnight as long as your journey on it started (or in the case of a delayed train it was scheduled to start) before midnight.

Any subsequent changes of train after midnight counts toward the next day’s pass use.

You cannot travel beyond midnight on the last day of validity of your pass.

What you mention in times is very daft simple IMPossible-even with fastest trains in the day you cannot do it that quick. Also do note that the direct INTernat treni dalle IT per FR and even more that nasty €* to LON require advance RES=booking with a hefty extra to pay. Perhaps even more as a cheap airticket dalle Malpensa would cost. There is NO overnight treni you could sensibly use between these 2. So I had to stay overnight in Brescia last autumn in a HTL close by the stazione.

First learn how to do it and start with using some travelplanners-better not in the app, but like bahnc.om, works for nearly all of EUR. Just see how it goes and where to change etc. Most likely you are by now waaaaaaaaaaaaaaaay too early to see times for summer, just use a samedayofweek to get a global idea. Your TrenIT-if they do not do this scioperta-is always very late with publishing final times.

To answer your question you simply need to understand how the mobile pass works. 

First you add each train you plan to travel on to your Trip. This can be done from the planner or added manually. You do not need to activate the pass at this stage.

Then on the day of travel you simply transfer the first train to your pass by the virtual slider (only appears after you activate the pass - again the advice is to wait until the first day just before travel).

This creates a QR code for the full day and a list is displayed below the QR code of the first train you plan to travel on. This is now your valid train ticket for that train. As you board further trains scheduled to leave before midnight on that day you follow the same process so they are added to the list below the QR code. Again this is now a valid ticket for that train. 

This becomes the process for all subsequent travel days,

If you transfer a train and then change your plans they can be removed from your pass by operating the virtual toggle again.