Visa extension timing

My husband was given a 30-day tourist visa to visit me while I am on business trip for 3months. We want to extend his visa for another 30days. If his 30 days will expire on July 15 w/c is Sunday, can he apply for visa ext on July10 if the processing time for visa ext is 5days? This is so he wont lose the whole 5days in his current visa. What will happen if his visa ext will only be released on July 18?