Q2 visa intervals between two entries

My husband is on Q2 and want to stay in China for about 6 months. His vias is multiple entries. 120 days/entry. So to stay for 6 months without the process of extension, can he exit to a neighboring country and reenter the next day? Does the timer always restart from reentry or is there any requirement on the intervals between two entries? Not seeing any information regarding interval requirement. Maybe I am just over thinking...