No now is not a good time. Next spring would be better but only if they need it. If they grew a lot this yr they probably don't need any.

Potted trees are way different than in ground. Potted needs at least monthly fertilizer. In ground trees probably need fertilizer in many locations depending on competing vegetation and other factors. But many people over fertilize. Fruit trees do best with moderate vigor. High vigor can reduce fruit quality, increase fruit disease pressure like brown rot, and needlessly increases pruning needs while shading out fruit wood lower on the tree.

Read the tree and fertilize accordingly. If growing adequately little or no fertilize is needed.

Too much nitrogen fertilizer can cause the tree to give less fruit, so it may be better to apply the fertilizer just after the fruit has been harvested.

For young trees (less than 4-5 years old), it is best to allow them to grow, and trying to get the tree to produce large amounts of fruit at this stage may not be the healthiest for the tree.