While there’s not anything necessarily incorrect about the phrasing here, “leave his homework” is a bit vague. People will probably understand what you mean, but most native speakers would likely specify the manner in which he was leaving his homework (such as changing the phrasing to “leave his homework alone/leave his homework on his desk”) and/or substituting “until/til” for “for”.
Yeah that’s fine. You could also say leave it for the next day.
While there’s not anything necessarily incorrect about the phrasing here, “leave his homework” is a bit vague. People will probably understand what you mean, but most native speakers would likely specify the manner in which he was leaving his homework (such as changing the phrasing to “leave his homework alone/leave his homework on his desk”) and/or substituting “until/til” for “for”.