Nap training: separate or same time as night training?

Our little one is 4.5 months. He’s a decent sleeper at night. Getting him to sleep can take a long time, but once he’s out he’s out—waking up once or twice to eat before up around 6:30.

But naps! He fights them so so hard. It often takes 45min or longer to get him down… and then he usually just sleeps for 20-30 min. He takes 3-4 naps a day. He would get so much more rest if he could connect his nap sleep cycles.

My question is: do you sleep train for night time and naps at the same time? Or are you supposed to start with one or the other?

Also, we use a SNOO for nighttime and most naps. Any advice on how to train in the SNOO?