When to slaughter/butcher to avoid flies outdoors?

I am failing on my google searches for this simple answer. I would like to slaughter and butcher our first pig this saturday (kunekune). The weather forecast is 62 F high / 39 F low slightly cloudy with 10% chance of rain. Is that just cold enough to avoid the flies or should I postpone it? Thanks!

I recently helped process some chickens about 3 weeks ago, and now that you mention it, I remember the flies focused on the chicken heads and blood in the bin of compost directly beneath the kill cones. The flies also had interest in the discarded innards, but I did not have any problems with them buzzing in my face, or landing on the carcasses or knives as we cleaned the chickens. The fresh chicken carcasses, to my surprise, really had no smell (it was my first time processing chickens). Maybe they would have been interested in the carcasses if they didn't have something else to land on. I'm guessing that if you have some pig blood and guts somewhat proximal to your processing, they'll be busy with that and leave you alone, but watch them make a liar out of me :) . I say go for it!

65 degrees f is cold enough to stem fly activity. Flies tend to head for the stink, so all parts of an animal that have the highest odor levels will be where flies head first.

There are two reasons animal harvest is traditionally done in the fall months; 1st  the air is cooler and thus helps animal carcasses cool faster.  2nd the cool air slows or stops flies from being a large problem.

What's about the hour of the day? Are they as active with electric light?

The general rule is that flies are not active at night. This might not hold true in tropical areas.
Most insects will be attracted to the light source, so if the light source is far enough away (Like a street light) you should have fewer issues with insects at ground level, reflected light will act similar to the actual light source though.

Yes, I kill kuys early in the morning as it does not take day long! Even with day light, there is much less.
With a head light, they come into the eyes, so I agree also with having the light a bit further!

When we butcher chickens which is often even indoors we had flies bothering us a large box fan with a good air flow works wonders as flies cant deal with the wind produced by it and wont be as likely to bother you, also butchering larger things like hog, beef, and deer it is ideal to do in the colder months or with a freezer or cooler to chill the meat we let our stuff hang ive left a rifle season deer hang for 3 days in almost freezing temps to stiffen it make cutting it easier although your hand freeze. But if you cant allow it to hand an need to butcher in the warmer days a fan is best to keep the flies at bay.