When does the 3 hours NICU schedule leave my baby’s internal clock?

My guy was born at 28 weeks, he is 7 months old, 4.5 months adjusted, and we are still up every 1-3 hours with him all night long. He has never had longer than a 3 hour stretch - not once!! We feed him full feedings every 2-3 hrs during the day and he is gaining good weight, but we are dying for more sleep. It feels like we are still in the newborn trenches month later. I am not opposed to (gently & safely) sleep training but he still seems too young.