Yes it is OK to fertilize while fruit is still on the tree. Fertilizing can be done with fruit or no fruit on the tree. However, in your location, I would hold off on fertilizing until Feb. 1st. It is important to understand that warm weather temperatures, not irrigation of fertilization, play the MAJOR role in stimulating untimely winter flushes of large mature trees. However, when unseasonably warm temperatures occur, young tees may flush more easily than larger, mature trees, especially trees planted the previous year. If such young trees flush during winter months, fertilization may simulate additional tender growth, making trees even more susceptible. Consider the degree of flush, tree size, time of year and geographic location, when making this decision.(Florida dooryard citrus guide).