I would say this is a highly location dependent and potentially status dependent thing. I have had very good luck across WOH and other programs checking in early without having to pay. Especially destinations where I arrive early in the morning ( Deep South America or Europe ) I think only once I was told I could pay to check in at 5:30 in the morning or wait until 8:00 in the morning to not have to pay ( this was at The Edition Abu Dhabi ).