I would be driving back on Monday so i am hoping the traffic won't be that bad on the way back from Sedona to San Diego.
I am narrowing down on the following plan. Please please comment if something does not sound right.
One additional question i had was about Joshua Tree park. Is there a specific entrance which gives the best view of Joshua Park. If i enter from Cottonwood Visitor Center area which is near to I-10 would i be missing all the good things? Also are there some trails where we can drive or carry the baby in the stroller?

- Start from San Diego at 6am and take I-10.
- Reach Josua Tree park (Cottonwood Visitor Center) around 9am or so. Spend 4 hours in Joshua Tree park.
- Leave around 1:30pm or so from Joshua Park towards Scottsdale.
- Reach Scottsdale at 6pm. Please let me know how is the I-10 route near Scottsdale. If it is okay to drive there till 8-9pm and night driving is not risky we can spend more time at Joshua and start only at 3pm.
- Spend the night at Scottsdale. Go around the city next morning and drive to Flagstaff via Sedona.
- Spend Fri/Sat/Sunday night at Flagstaff. Plan day trips to Grand Canyon and may be even to Sedona.
- Return back to San Diego on Monday.

The other option as someone suggested is to stay the first night at 29 Palms and visit Joshua tree park from there.
Then head to Flagstaff and make it the base for next 3 days and visit Sedona/GC from there. Or make it the base for 2 days and visit GC. On Sunday visit Sedona and come to Scottsdale for night stay and then happily leave for San Diego on Monday noon or so.

Thanks a lot for everyone's help. From zero i find myself to be little more educated about the area.