How long did it take toddler to transition to new bed/new room?

My son is 2 years old (27 months) and I’m pregnant with baby number 2 in January. He is still in his crib and I’m so nervous to switch things up on him but we do have his new room ready. When I talk to him abt moving to his new big boy bed he gets upset and he wants his crib. I really don’t want to buy a second crib. When should I start the process? And how long did it take for your toddler to adjust?