How long decision in process normally takes? I have submitted a manuscript to a journal on September after few days the status changed to under review and after 5 months the it changed to all required reviews are completed and immediately to decision in process. It has been 3 weeks that the paper status stuck at decision in process. How long this stage normally takes ?  is it too early to ask the editor (?) about the status of my paper?
No, it is not too early. "Decision in progress" means all the reviews have already been received and what's left is for the editor to make a decision. 3 weeks is pretty long for this. I would write to the journal asking for a status update.