Ok, so if he is only used to 2hrs A time in the morning, you don't push to 2.5hrs right away. You push slowly and add 10-15mins every couple of days.
At 5 months, the ideal routine is 2 long naps (1.5hrs) and a catnap and your day would look something like this:
7am - wake
9.30-11 - morning nap
1.30-3 - afternoon nap
5.30-6 - catnap
8pm - bedtime
He will be sleeping 3.5hrs at night and 11hrs at night, which is about right
When he is able to stretch to 3 hrs A time, he will then be on 2 naps and his day will look something like this:
7am - wake
10-11.30 - morning nap
2.30-4 - afternoon nap
7pm - bedtime (earlier bedtime because there is no more catnap)
So, if you hear him at 6.30am and his morning nap is at 9am, then you wouldn't need to stretch him in the morning and you just have to work on the afternoon A. If his afternoon A is only 2hrs at the moment (sorry can't remember what it is) and you're getting a short nap and he's waking up happy, then perhaps he needs more A. Or if its already at 2.5hrs A time, he may need even more A or he may need a shorter morning nap. I did both... stretched A to 3 hrs and made sure morning nap wasn't longer than 1.5hrs. Unfortunately there is no right or wrong answer, it is about working with your baby and seeing what works best. You can try not letting him sleep more than 1.5hrs and keeping his afternoon A at 2.5hrs to see if he will sleep longer in the pm. Try something for 3-4 days before seeing if its working or not.
Here is a link to the 3-2 nap transition, which will explain what he will probably be going through over the next couple of months.
All about the 3-2 transition- 5/6 months