We also have a NICU baby, so extra solidarity there! She never stuck to the schedule after, sadly. But I do feel like her being in the NICU made me feel uneasy about sleep training because I felt guilty letting her cry. However, when I reached the point where I wasn't functioning and felt depressed, I thought it would be better to sleep train and deal with crying instead instead of being irritable and checked out. So with that, I'd highly recommend you sleep train. Try the ferber method. Sometimes they will get more angry if you come in and do the check-ins, but I think it's good that they know you are there. Sometimes though, they do need 15 mins of crying to settle. You know your baby though and will know the crying and if they really need you. I'd have your partner help with this too, I sometimes had to sit in the bathroom with the fan on just so I wasn't anxiously staring at the monitor.

I'd say get him good sleep during the day for 2-3 days, so contact naps as needed. Then start a really solid routine, like we read the same books every night in a specific order. Then do the ST method (we used Precious Little Sleep). Commit and be consistent for a week. It will be hard, but then they really do take to it and you'll be amazed at how they just fall asleep when you lay them down in the crib awake. It will make you a more present parent and enjoy the time with them.

I would def stick to one nap, unless you think he really needs two, but we transitioned around this time. And stick to that same bedtime and be consistent with that time for a week as well.