I had one take 3 days, but I put the horse up at night. After that, once in a while the horse would whinny and act silly and about 30 minutes of being tied up and she just propped up a hind foot and went to sleep.
I have tried to have 3 or 4 hours as a minimum time to keep a horse tied up. If a horse is tied up for 4 hours and is still throwing a fit, and you put him up and tie him up again tomorrow, I do not think it changes the dynamic. I do not think it hurt a thing if you go right back and do it again tomorrow. At some point it will sink in that there is life after separation.
I have found the safest place to tie one is to a rope hanging down from a tree limb. THE ROPE MUST HAVE A GOOD SWIVEL SNAP IN IT. They will go around and around and paw and whinny and throw big fits and when the dust finally settles, they will all 'give it up'.