Hi Jeff, as o9o said there isn't really a beekeeping Calendar, there are approx times of year when you might consider doing certain things, depending on many things.
When I might Feed syrup falls into a few occasions during the year, when I can't say right now other than they are seasonal and dependent on the colonies needs.
Pre winter feeding if required which usually occurs late summer but only whilst temperature is still high enough.
Spring build up if required which would happen when the temperature is high enough for them to process it, but lots of pitfalls with this one, the bees need space to expand for instance so pointless filling it all with food and of course you don't want it in your honey crop being just 2 of many.
The next being to feed hungry bees, typically a swarm a few days after they have been housed or a split which can't necessarily forage for themselves, or of course during bad weather or breaks in available forage.
Also syrup can be fed when you want them to produce wax, draw foundation, build comb etc.
For now keep hefting and ensure they have sufficient stores to get to spring. When the time is right in spring your first quick look to assess what you have will tell you when the time to feed syrup is, or isn't. Fine balance spring feeding.
Good luck, the above works for me and my bees but other views will be along soon.
Oh to answer your question..... Feb, March, April, May, if required and depending on weather and space and colony size and .............