With regard to the social interaction rules in the DMG (which I use a lot to adjudicate challenges), by design it looks to me that you have a chat with the NPC to try to improve their attitude, sussing out the NPC's agenda, ideal, bond, and flaw for advantage if you roll, then you make the ask, which is cross-referenced with the DC table. There is notably nothing that says what level of effort (or successes) is needed to move an NPC from one attitude to another, even temporarily. How hard does the party have to work to turn a hostile creature friendly? This is left to the DM to decide. For my part, I tend to create specific objections to be overcome by the PCs and then if the PCs overcome most of them, it shifts the attitude. Each attempt to overcome an objection may call for a roll or not as with any action declaration.