When can cattle feed after spraying?

It's not really a good idea to do so, no. If you read the label on the container, it should say that you should not allow grazing access to the area you sprayed for 20 to 30 days. Of course that more applies to full-field spraying and not spot-spraying. With spot spraying, it's probably best to prohibit them from grazing that area for at least a week.