There isn't a better moment for it. Or there won't be, if they get the chance to force him. Being forced hurts.
The adrenaline rush that comes from transforming in front of people for the first time in twelve years almost knocks him over, though he manages to turn it into a willing kneel instead of anyone realising just how weak he is. These people, he'll kneel for.
"I'd appreciate diplomacy, myself." He says, trying for light-hearted and falling flat. His voice sounds like sandpaper.
Unexpectedly Remus' wand arm quivers and droops instead of the immediate curse Sirius had been expecting. His mouth has fallen open, whether at being right or Sirius' own willingness, Sirius couldn't tell.
In contrast Nem trips over themself to hug him. They're crying. Over him. Over him being here. It takes too long for him to remember to hug them back and by then Remus has recovered.
"Get away from him." Remus says sternly, only the faintest quiver in his voice. This must be so hard for him. "We need to alert the ministry."
"We won't do anything of the sort." Nem says, equally stern. Sirius pushes himself out of their arms; he won't have them getting caught in the fire if people decide to start firing.
"Let me explain first please." He says, gesturing at the photo Charlie is still holding. "Please Remus."
"You betrayed us. I owe you nothing."
"Of course you don't." He replies, surprised; he never thought they owed him. This was all his fault, he knows that. "But I never meant for this to happen, and Remus Harry isn't safe, I have to…"
"DON'T YOU DARE SAY HIS NAME!"
Sirius doesn't doubt that the spell that shoots out of Remus' wand is involuntary but that doesn't prevent it from hurting.
"I won't. I won't." Remus is right anyway, Sirius does not deserve to say Harry's name. "But he isn't safe."
"The only thing he's in danger from is you." Remus spits, but Sirius pleading retort is lost in Nem's laughter.
"How is anyone under any threat from Sirius? He's been doing nothing but keep me company all year."