The actual commute time will be about 35 min to an hour, depends on how fast you can catch a bus from Dolphin. If you miss the bus, you need to wait max 15 minutes for the next one. Once you get on board, the travelling time will be about 25 minutes.
Disney transportation system begins an hour before parks open.
The breakfast at Ohana and Chef is from 730 till 11, or something close to that.
What time to set the PS for really depends on what are the available times you can take, how early you wake up, and how early you want to get to the parks. PS for these can be made 120 days prior to the day of your dining.
We had breakfast at both places at 9am during our honeymoon trip. It worked well for us.
If you wanna to check the commute time in between places in the park using Disney trans, I highly recommend this website for you:
Transportation Wizard
This tool provided at this site gives you a rough estimate of your commute time and helps you to plan your trip better, especially if it is your first visit. At least it did help me for my last trip. Disney transportation is very easy to use and gets you everywhere in the park. If you got lost, just ask the cast members near by and they will give you directions.
Hope it helps!