Baby who only takes 30 minute naps

Good morning,

I am writing to you because my 5 month old baby only takes 30/40 minute naps (4 per day). He wakes up very grumpy and we can see that he is still tired. We have to take it again to make it prolong its cycle (which doesn't always work....). On the other hand, at night we put him in bed at 7:30 p.m. and he sleeps until 4/4:30 a.m. and then sleeps again until 7/7:30 a.m. How do you get your baby to cycle through naps? Should we let him cry?