Setting a timeline for when a war will end is cursed logic. Its guaranteed to never end at that time. Especially since by early May, the Ukrainian Army will be reinforced and rearmed. With Kiev and Kharkiv no longer under pressure, they will be free to replace those defense lines with draftees and send their professional force over the Dneiper into Kherson and Donbass.
Also, By May, Russia will be out of refined petroleum. Its mind boggling considering how much petroleum Russia has, but they have very little refinement capacity, and their ability to move refined product to where its needed is severely hamstrung at this point. Its why the Russian Airforce is MIA right now. They are out of Aviation Fuel. By May, if they are to maintain operational tempo they are going to have to start rationing civilian use of refined petroleum. Or else abandon mechanized warfare entirely.
Ukraine knows this too. Its why they are so busy trying to blow up fuel depots in the border regions.