I suggest emailing them directly advising them of your arrival time and asking / offering to buy the night before if necessary. I have had direct email correspondence with this hotel over the last couple of years as Covid caused me to keep rescheduling, then when I could travel they closed for refurbishment. But they have always replied to my emails very promptly (allowing for timezone). A few months ago I stayed at the Westin (Marriott was closed for refurbishment) with similarly early arrival time and they had no problems with me checking in at that time of the morning. As it was during the period of testing-on-arrival and staying in your hotel room until results came back, all hotels had to track this and so they proactively reached out to ask for my arrival time.