From scratch it would take several years. At least in my country, to train a pilot you have to go to the Military Air Force School to complete an 8 semester long career that won't necessarily grant you a position as a pilot. Of course, with constrained times of war, this can be achieved in less than 4 years, but 1 year seems like a stretch. Now, if you have a vast disposal of trained pilots, I guess you can make it in one year or even less, depending on several factors. The problem is I don't find stats about this case, and even if there are a lot of Ukrainian pilots ready to fly, they are probably not seasoned in combat.