I'd like to get some pointers for running one-shots with Agon.

How long do you expect a one-shot to be for Fate to be relevant and for characters to retire?
Can this actually happen within one session or does it take at least two sessions?
How much gametime is usually necessary to conclude a simple 3-objectives quest? One hour per objective?
Are there any rules one should use for a one-shot, like, for example, making everyone half-divine? Or extra Strife for the Antagonist?

I am also thinking of ways to make the rules more accessible. I will probably use cards to write the stats for each weapon and I will write on the range sheet the penalties for attacking outside of optimal range. Got any extra tips?

Fate: while it is possible for a player to burn through their fate in a one-shot (whether one or two sessions), it's not likely.
This doesn't matter though - just let them use it. The things it can be used for in an one-shot adventure will just help keep things moving nicely along (removing wounds and impairments will mean fewer interludes).
Alternatively, you could just say that since its a one-shot, the fate rules aren't being used. It won't hurt the game much either way.

Character retirement is something that is rare (in my experience) in the course of a single island - it takes several islands, with three quests per island. That could be a lot of sessions.

Time to complete a simple 3-objective quest: you should be able to manage this in one session, even a short session, if the path between objectives is clear.

Apart from possibly the fate issue you mention above, there's no area of the rules that needs tweaking for a one-shot. I wouldn't suggest making everyone half-divine unless they all leap at it - if anything, I'd suggest making everyone ordinary humans, so they get an idea of that starting power level and can appreciate what half-divine actually means once played in the context of a longer term game where fate is relevant.

For running it as a GM, I would recommend having some kind of record where you can make a note of how each npc and minion group have allocated their weapons, with enough rows that you can change this each round. This was the big headache for me when running multiple enemies.
Also, having a sheet which allows you to record initiatives (including the weapons used) of each person.

That's all good advice, Darren.

Rick, check out the "One Shot Scoring" page on the wiki:
http://random.average-bear.com/Agon/OneShotScoring

There are a couple of ideas there about changing Glory rewards for a one shot to make Fate a more valuable commodity.