Hello Krzysztof,
There isn't really a "wrong time to harvest" per se to your question's direct concern nor how long the timbers sit...
Each timber framing culture has its own "best practices" within a spectrum of what is know within timber framing. For the most part, timbers are "green" when worked.
Your schedule may not be optimum, but I would offer that you have little to worry about if the timbers sit for a few months (or even years) as long as they are end sealed and keep out of direct sun light and/or moisture. They are typically large enough to not dry to terribly fast, and if end seal, this even retards the drying process further.
I would suggest that your schedule (in this case) can take precedent over a best time to harvest. I worked with Picea Abies (Norway Spruce) a few times and I personally like the wood very much. It can be challenging like Tsuga (the Hemlocks) yet its grain patterns are most pleasant to most the like Confer species...
Good Luck, and keep us posted on your progress...
j
Last edited by Jay White Cloud; 01/24/19 06:54 AM.