You can still eat the eggs after making the switch, there isn't a withdrawal period for switching feeds.
After about a week, the eggs shouldn't contain anymore soy. At this point the hen's system would be completely cleared of the previous feed.
A pullet is hatched with all the eggs she will ever have. More than she can lay in a lifetime.
The follicles start growing into yolks in a type of assembly line in ever increasing size, so a hen in lay, may have about 6 or more growing yolks and after a mature follicle bursts and drops the yolk into the infundibulum, it will be about 25 hours before it is laid so I would suspect perhaps you'll have to wait till you get as many as 10 eggs before there is little chance of soy being in the egg.