Hakone Free Pass/Romance Car

I need some information on the Hakone Free Pass and the Romance Car.

My family of 4 is planning to do a overnight trip to Hakone using the Romance Car from Shinjuku station. I understand that all seats for Romance Car needs to be reserved. I know which train I want to take from Shinjuku to Hakone but since I don't know the exact time we’ll be leaving Hakone on our way back, how should I reserve our seats for the Romance Car for the return trip?

I also understand that the Hakone Free Pass is good for 2 (or 3) days. Does this mean 48 hours or does it mean 2 days no matter what time you buy the pass? 

You can reserve your Romance Car seats online for your return trip and buy the tickets at the station on the ticket machine or at the ticket office. And you’ll be able to change your reservation if it’s before the time of departure of the train you have reservations for, but only if they have seats open on the train that you’d like to change to. Please note that for reservations made within 7 days of the reserved train date, if you don’t pay for the reserved seats 15 minutes before the train departs, your reservation becomes cancelled automatically.

The Hakone Free Pass is good for 2 calendar days, not 48 hours from buying the pass.