I have four horses to bring in every night. I have hay waiting for them and that's it.
They do not get their supplements until I have closed the paddock gate and done a couple other things in the barn.
I might give them their supplements right after closing the paddock gate, or I might not.
Point-being, they know they'll get their supplements but they aren't sure just when. I keep them guessing because they are all smart enough to know, if I do things precisely in XYZ order every night - they are getting their supplements when "Z" is complete and they start being snotfaces somewhere between X & Y.
Even at that, some nights somebody will get testy and I will charge at them, loudly saying "NO!" It's very rare that I have to hold somebody's pan back because they refuse to be mannerly but I have done it and they don't get their pan until I have counted to ten and they're still behaving.
Sounds cruel, I know but I have only have about four rules in this life and being mannerly is one of them
Let your horse have his hay and water. Once he settles down to being a gentleman and patiently waiting, then he can have his supplements.