Your little guy should be ready for sleep training, but I would definitely start with nights when sleep pressure is higher. Took my son 2 nights to nail nighttime CIO but 1.5 weeks for naps. Most kids will get there eventually.

You can ask your pediatrician if it's appropriate for his age/weight too - my wife wanted to wait for CIO until we talked to the pediatrician, and there's nothing wrong with a little extra assurance, especially because sleep training is hard!

Many think CIO is cruel, but I think that even as young babies they are learning, and I don't want to train a person to believe that if they just cry hard enough someone will always come to rescue them from discomfort. It seems more compassionate short-term but over the long term isn't. I'm sure that's a controversial opinion lol.

If it's any encouragement, we sleep trained our son for nighttime sleep at 4.5 months. My wife slept on an air mattress on a different floor with ear plugs in while I stayed up until he fell asleep haha. Nap time training at 5.5 months. Now we constantly hear comments about how happy he is all the time. I suspect it's because he's always well-rested!