I haven't tried this as of late, but I remember once messing around with the booking system a couple of years ago and I too got the "3 hour" issue when attempting to book a flight within that time window. So I'd say this has little to do with the pass and more to do with how the system handles such bookings. The "free same day change to an earlier flight" via comfort flex and business class tickets seems to be actually not impacted by this rule though.
Of course where the booking system can't help you, customer service usually can (and the airport agents even more, those at the hubs probably more than others), but of course the fee should be waived (or the "0 day" pass should be renamed to "3-hour pass" ​​​​​​).