I'm not sure really - I always gave mine a real pampering after being ridden and often played with mare in field a little (she liked messing around trotting after me) so never fed sooner than an hour after riding anyway
As long as the horse has cooled down, breathing returned to normal etc then it should be fine, obviously if horse has been worked hard and still puffing etc better to wait a bit.
Depends on how hard I work them. If I ride my horseys hard and the are sweating and puffing (even after a considerable cool down) then I wait until their temp is alot lower and their breathing has returned to normal.
If I ride them just for a little hack, or light schooling, I get off them, untack them, groom them off, rug and then feed, so that takes about 15mins.
Usually wait about 20 mins or so to give Ellie chance to cool down before I feed her after a hack but if we've been jumping I give her longer as she gets a lot hotter then
I always wait at least 1/2 hour before feeding, I give him a small haynet while I groom him then sort my stuff out then feed him so thats about 1/2 hour, I take my time!
you should not feed really for an hour before work or for an hour after work. dont feed before work due it can give them colic if you can image you tighting up a belt on your trousers tight after you have eaton it hurst. dont feed after work coz they can joke coz there breathing is not normal it can cause choke and dont give cold water for at least 30 mins wait for them o call off or you can send them in to i state of shock trust me i have seen it done!