To walk from our hotel at Marriott in Puxi, how long would it take us (in minutes), to reach Peoples Avenue so we can take the tour bus on time?

I am wondering whether you refer to Courtyard by Marriott Puxi Hotel? If so, you may need to walk around 45min or a little longer to your destination.

Actually, your hotel is within 3-5min walking distance to Hanzhong Road MTR Station along subway line 1. By MTR, you can reach People's Square within 10-15min.