Well, yes, most often they are usually regurgitated within the third day, but it being the fourth is certainly within reason too.
Regardless of the amount of days it took for this to occur, there is definitely a problem of some kind. Either the meal was too big, temps not warm enough, it inadvertently ingested some fecal matter from the substrate or water bowl, or a possible combination of any of those. They can also regurge if handled if they are fairly nervous too, but from what you are saying, I doubt that has ant relevence at all with this particular situation.
As you may already know, the very LAST thing you would want to do is offer the snake another meal anytime soon. The snake needs to replenish it's stomach acids, electrolytes, enzymes and proper gut flora before it can properly digest it's next meal.
Yes, you should most definitely wait a good 7 to ten days before attempting to feed it again, and when you DO, make sure it is a much smaller sized meal to see if this is digested. After a few smaller meals, you could then gradually work up to a more normal-sized meal if all seems okay.
If it regurges the next smaller meal after waiting the 7 to ten days, You should immediately seek a qualified reptile vet that can administer some medication to combat the problem. I have found that when bad gut bacteria is present in their intestinal tract for any number of the above given reasons, a two-dose regimen of "Flagyl"(metronidazole) given at the rate of 50mg/per kg of body weight, and another follow-up dose in 10 or so days after the initial dose works absolute WONDERS if intestinal bacteria is the root cause of the regurgitations, and snake's I have personally dosed in the past never had another regurge issue whatsoever from that day on!!.
It is VERY important however that if this is medication is administered, you do NOT feed the snake at ALL until approx. 7 to 10 days AFTER the last dose was given because this medication also kills the "good" bacteria flora that the snake needs to properly digest it's meals.
Additionally, Flagyl is very reptile friendly, so there is no worry about any negative effects from these doses either. If you cannot seem to find a vet that is well-learned in reptile medicine, I would copy the dose exactly as I mentioned above so they can give it the proper amount of medication, even if they do not know what to give it, or how much.
First though, the snake should definitely have a "fecal floatation" done by the vet BEFORE any course of medication can be taken, so he/she knows exactly what is the cause and then know the best course of action that should be taken.
Anyway, I would look into any of the above husbabdry possibilities first, and then go from there, but I would first give the snake 7 to ten days of no food, then offer the much smaller meal to see how things go with those first. But if the snake has problems after the next few smaller meals after the 7 to 10 days, you should make a bee-line to a qualified vet ASAP!
good luck with it!
~Doug
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"a snake in the grass is a GOOD thing" 
my website -serpentinespecialties.webs.com