Yes, you can. Happy travelling! :)

Thanks.
What are the closing hrs. of Beihai & Jingshan parks? From Forbidden city, which exit should I take to visit Beihai & Jingshan?

Opening hours of Beihai Park:
06:30-20:00 (January, February, March, November, December)
06:00-21:00 (April, May, September, October)
06:00 to 22:00 (June, July, August)
Opening hours of Jinshan Park:
06:30-19:00
After your Forbidden city visit, pass the north gate: Shenwumen (Gate of Divine Prowess), Jingshan Park is on the north within walking distance.

Thanks for the useful info. How many hours should I spend seeing the Forbidden city?
Can I walk to Beihai park from Jingshan park? Thanks.

Forbidden City is a must-see to explore. Tourist can even spend one day to visit it. However, if you are not that interested in it or you have no much time, half a day is what i suggust.
You can walk to Beihai from Jingshan. They are within walking distance.

Thanks Melissa.
How many hours should I spend at Jingshan hill & Beihai park? Thanks again.

You can spend 2 hours in Jingshan and 2 hours in Beihai, or say, half a day in these two sites. So, you one day visit will be cut into Forbidden City half and Park half. That's reasonable and popular route. Enjoy :)