When when when?
When is the right time to plant? When is the right time to fertilize? When is the right time to mulch? Etc etc etc.
answer: always
What??!!
Different zones, different plants,crops,legumes, etc
Soil needs feeding always, especially when it is providing nutrients for large plant growth cycles.
Research guidelines for plants you have growing, understand soil enzymes are more active during longer warmth and light periods but is active even with snow on the ground. A little reading goes a long way.