feed grain in the middle of the day after a workout, the answer is no. Horses should be kept on a fairly ridged time table for feed (an hour either way should be the maximum difference).
Sorry I tend to disagree.... I find that it is horse that are kept on such a rigid schedule as you describe will actually colic, or have issues then those that are not.
If horses are fed w such rigid routines, its when something unforeseen happens and they get fed out of the norm, their systems go into complete "shock" so to speak, and will end up having more episodes of colic, or tieing up then horse w a more relaxed schedule.
Our horses sometimes get their am grain at 630 (summer hours), and in winter as late as 9:00am. There evening grain can be anywhere from 3:00pm to 6:00pm.
I have not had any colic issues or tieing up issues, or adverse effects from such, as our horses aren't so used to a exact feed time that their systems don't go into shock the minute something is different. Horses are hardier then we give them credit for.
I do agree that your feedings should be spaced out appropriately though. So if you want to add a noon feed, talk w your barn Manager and see what the routine is for feeding in am, and you can adjust accordingly.