Hi, my 5 month old was exactly like that. Great night sleeper but from 7am till 9:30pm just fought sleep. What I tried to do was get into a bit of a routine. After he woke in the morning I put him back down to sleep a lot earlier than I used to. Usually around 1-1.5 hours after he woke. I put him down awake and to my amazement he put himself to sleep. It took about 20 mins but he didn't cry at all. Just made a few noises. He would always wake up after 1 sleep cycle and I tried to resettle him preferably in his cot. I tried a few different methods of resettling before finding one that worked for him. Then when he was next up I did the same thing. Initially putting himself to sleep got harder as the day wore on but pretty soon he got the hang of it. It took a couple of weeks for him to get the hang of reseetling himself after the 1 sleep cycle. I initially only let him stay up for 1.5 hours at a time and as he got used to this routine he seemed to be able to recognise tiredness better and his tired signs became more obvious. He soon became able to stay up a little longer. If he got to 2 hours without tired signs I would put him down awake anyway. I do the same routine whenever I put him down. Take him into his dark room. Tell him it's time for night nights and mummy loves him and give him a cuddle. Put him down and put him in his sleeping bag. Pick him up and cuddle saying the same as before. Put him down. Tell him "I love you, Have a good sleep. I'll see you after" while stroking his hair and kissing his forehead and then leave. He doesn't cry at all.

He's now used to his routine including that he is put down for sleeps roughly the same time each day. I've done this at various peoples houses too with the same routine and he will fall alseep. I'm stunned cause he used to be exactly like your little one.

BTW I used to get the comments about being a great night sleeper and to stop whingeing but it is so hard having a bubs who doesn't sleep during the day and gets crankier and crankier! Good luck.