Chicka, is there any possibility that you have two different types of tree blooming there? Most fruit trees, both the fruiting and the ornamental varieties, are grafted onto rootstock of a similar but hardier species. Some have two grafts, one of the root to the trunk, then a second of branches to the trunk (that is most often the case with "dwarf" varieties). If the damage from the Roundup caused branches to grow from the rootstock, that could account for the different bloom times.
A good example of what I mean can be seen with a tree that has been very popular in landscapes - a purple-leaved plum called "Thundercloud." You can often see sprouts coming up from the roots that have green leaves. If something happens that causes the top of the tree to get broken or otherwise die back, what grows back will have green leaves; that's the rootstock growing.
