Oriol, the host, was very accommodating. I messaged him that we would be arriving really early and if he could let us leave our bags first and just come back at the allowed check-in time. Not only did he reply quickly, he also met us at the apartment and let us in (even helped us carry our bags!) and already check-in and stay.
He then gave us restaurant recommendations, transportation and places to see suggestions, too. Which wasn't really a big problem as his place was about 15 minutes' walk to key areas like Ramblas.
The place was very clean and comfortable, too. It has an elevator so it carrying your bags to the 2nd floor apartment wasn't a problem.
Will consider staying here again next time I visit Barcelona.