I’m so so bad at this. 
I have a good friend who wants to visit today. Problem is that when she visits she stays for hours and hours and never leaves. It’s painful.
I have two very young children. I do their tea at five and then bath then bedtime routine. If my friend is present during this time, they will carry on and not eat and not settle and it’ll be the evening from hell. Voice of bitter experience.
Problem is that friend (who lives in a different town) has something on local to me at seven o’clock so I think she is envisaging staying till then.
Would it be really bad for me to say to her yeah come over but I need you to leave before five?? Obviously I’ll think of a more polite way to phrase it 