How do I make: Chicken feeding bin

This is a lot more complicated than it sounds, but not totally impossible. 

• You'll need to either make multiple blockstates depending on how full the bin is, (if you want filling it to change it visually), or just make it a storage block.
• For attracting chickens, you'll need to run an entity iterator that makes all chickens pathfind to the block within a certain radius, and then checks for chickens directly above or adjacent, (or within the block's hitbox if it's only partly solid), subtracting seeds from itself. I'm not sure whether the egg timer is NBT data; if it is, you can override it, but if it's hard coded, you won't be able to, and may just need to randomly drop some egg items when chickens eat.
• To do the cooldown timer, you could program in a complicated NBT counter... or just give the chickens a passive effect like 'Unluck' whenever they eat from the bin, (passive, so the particles don't show), then have the entity iterator first check they don't have the effect. I unfortunately use this workaround way more than I should.

I'd recommend taking a look at Quark's github if you want some pointers, they have a pretty decent animal feeder system.