do not write first, then talk to your boss honestly and frankly
tell him 由于 lp工作变动,我必须按时走去接孩子,其实我晚上还会干, you always make the time up. You always work more than 9 hours every day. You will work more, you want this company to succeed, if the company is good, you are good, blabla
You are on the same boat with your boss.
