I know you all had probably hoped for better progress, but 6-7 hours is only the average time, some people can take much longer. When a heart is on bypass the lungs don't work for themselves for quite some time, it's probably only that his just need more time to recover.
It's sad that you can't go and see him, I'm sure you would feel better if you could, but I'm sure your mum is telling you eveything that happens straight away so you don't feel too left out.
The most important things right now are that the surgery went well, if they're happy with that then that's a very good thing, and that he is awake and aware. He can write so his memory is working and he can control his movements too. These are all important achievements.
Hopefully soon his breathing will come back under his control, and then you can all relax again.
It's sure to be a tense time right now, but try to stay positive.
If there's anything I can do, get in touch anytime.
Take care of yourself Angel Girl.