How much of a head start?

Three minutes.

There's some sort of activity visible at the checkpoint down the road. Foot and vehicle traffic is enough that details are not super clear.

He will probably interact with the checkpoint later. For now he is going the other way.

The city has more little empty spots for the finding. Well, empty of everything except trash, for the most part.

The drizzle has stopped, and the sun is setting. There's significantly less artificial light in one direction than the others at the next intersection.

He will sit near trash. Demons smell worse. He can sit up all night, practicing Prestidigitation with motivation to keep him at it.

Big trucks with the ADVENT symbol drive by a couple of times through the night. As well as foot patrols of troopers, who everyone gets out of the way of. (Things are mosty but not entirely dead late into the night.) At one point a woman comes and tosses another bag on the trash heap. He is otherwise undisturbed.

He gets so much Prestidigitation practice done. By the time the dawn comes he has made visible inroads on a coin-sized puddle of trash juice; it's closer to the size of a crown than a copper, now. Probably much of that change is evaporation, but the main object was to stay awake for lack of a suitable place to sleep, and he has spent the time productively instead of having nonstop flashbacks, even.

When the sunrise begins he closes his eyes and clasps his symbol in prayer.

Activity picks up around him with the dawn. People and vehicles making noise.

Also, when he's most of the way through it, there's a loud explosion in the distance.

...it's not really possible to pray faster but he notes the direction, and when he gets up after his prayers he heads that way.

There are a couple more explosions and sounds of gunfire and fleeing civilians! A store is on fire and half blown up! There are people shooting at the ADVENT troops and the troops shooting back. Everyone is using large objects as cover. A few people are already downed. The troopers bleed orange.

He does not know which side of this fight to intervene on; he'd pray about it but that obviously wouldn't help. He finds a large object he can peek around and starts casting Stabilize.

He can reach two non-ADVENT (dead; stabilized) and five ADVENT (stabilized, dead, dead, dead, stabilized) without wading directly into the middle of the firefight.

The troopers attempt to dart to better positions in the chaos... But their enemy seems to know exactly when they're going to do this and already be aiming in that direction. The fight is turning against them. Even so, a flying black and red aircraft swoops in and disgorges a few reinforcements, including someone in fancier red armor with a cape.

An adventurer of some kind? Just one of them? Maybe the others find themselves still well served with standard issue gear.

If he's out of people to stabilize he will maybe create some water into the burning building, if it's not too far away.

There are lots of things burning right now, he's spoilt for choice. It doesn't seem to be spreading much, whatever all the buildings are made of it's not that flammable.

The firefight continues around him. Red Cape directs the troopers and they perform visibly better following his shouted orders. Things seem to be at a stalemate for a brief moment. Then, a thrown object starts emitting copious amounts of smoke and the attackers - wearing less armor and using what seem like cruder weapons - make another aggressive advance under concealment. Both sides are still ignoring him.

He should maybe have prepared any alignment detection but even if he knew which of these people were evil it would not in fact tell him much about who ought to be alive and who ought not to be alive. Stabilize. Create Water. Create Water.

Red Cape goes down in a spray of bullets and then it's all over for the ADVENT troopers, the remaining ones acting out in confusion. Though still with absolutely zero hesitation or fear. Three of the attackers barge into a nearby building and the other five still standing run to stand guard or go check their downed comrades. Two approach him, weapons pointed and shouting.

The fearlessness is maybe a paladin on their side, maybe Heroisms all around or something.

He holds his hands up.

The woman with a shotgun and a giant machete holds him at gunpoint and says more things he doesn't understand, while the man with an AR keeps watch down the street.

"I don't speak the language. I can cast Comprehend Languages," he says, those last words slow and clear in case they've heard the verbal component before.

Yeah no they don't understand and instead are just going to wait here, tensely. It'll be about one minute before the three who went into the building come back out.

Welp. He will hold his hands up and wait then.

The three who went into the building come out after a minute. Two of them are carrying a big torso-sized case between them and the third is carrying a woman who looks like she's been tortured - scars and injuries - in a fireman carry. The others go to pick up their wounded and dead and all retreat somewhere else.

How much do the people standing over him hate it if he moves one hand a lil bit.

Just a "Hey!". They're starting to back off towards the blown up store anyway.