Mine eat for a while then lard about, yesterday DD put them out at 5pm, they came in at 9pm (I was out late) they were quite active when it got later, pootling round.
YY to build up time, the lush grass is full of moisture and can give them a loose pooh as well as the risk of bloat.
They feed fairly contantly (that doesn't mean 24/7 piggies ) so as long as they have access to grass or hay, they'll pretty much regulate themselves.
We did cut out veg for supper when GP2 had grass, they were very judgey with hay and pellets but GP2 had an awkward bum.
Our boars were in holiday boarding (when we had GP1/GP2 then GP2/GP3) . When GP3 boarded he was under 3 months so his relationship with GP1 was at the crucial stage (aka young arsey boar ). I asked that they be kept away from girls for the same reason, they were and they were fine.