@Catherine2545 Hosts can send a request for additional fees via Resolutions, but they don't have the authority to collect the payment if you decline. Airbnb doesn't enforce arbitrary fees on behalf of hosts, even if they're stipulated in the listing - that's just not how they roll. If the listing specifies a time window for check-ins, you're obliged to honor it, but there's no rule about what to do if you can't.
What Airbnb can't do is force the host to honor the booking if you try to check in without having paid the late fee. If you show up on your arrival date at get turned away, Airbnb will eventually give you your money back, but you might lose a lot of money on the last-minute replacement booking.
If you happen to be within the brief grace period for free cancellations, I would strongly suggest cancelling this booking immediately. It becomes a lot more complicated if that's not the case - you'd really have to persuade an outsourced customer service operator who might not be fluent in English that you're being hit with undisclosed fees, and if your arrival time is outside of the window shown in the listing you won't have a leg to stand on. But whatever it takes - even if it means losing out on some fees - I would recommend cancelling this booking. Nothing good can come of a stay that involves a dispute before arrival.
Of course, another possibility is to pay the $50, which might be a reasonable expense for the privilege of arriving after the host's normal business hours. Airbnbs are not like hotels with 24-hour desk service; most hosts have to arrange their whole life and work schedule around your arrival, so if you want to come at an exceptionally late time, it's likely to be a disruption that comes with a cost.