Giving away a free oven cleaner is a clever trick, isn't it? I'm sure it's intended to make you feel that you absolutely must host this party
Even if everyone else in the world is willing to host a mid week party, that doesn't matter. It's your house, and it's up to you who gets over the threshold
Stay firm and adopt the "stuck record technique". Remember that any answer/excuse you might give, they will have an answer to it. The trick is to not engage in conversation. Don't give them anything they can latch onto
eg
No, mid week isn't convenient
Why not?
It doesn't suit me
Why not?
It doesn't matter why not, I've told you it's not convenient
What's the problem?
I've explained, mid week isn't convenient
But you promised to host a party
Yes, I'm willing to do that, I've given you three weekend dates when I'm available, but midweek is not convenient for me
Most people love coming out mid week, because it saves weekends for precious family time
Well maybe, but midweek isn't convenient for me. We're going round in circles here. I've explained that midweek isn't convenient. I'm willing to host a party on a weekend, but if that doesn't suit you, there's probably not much point in continuing this conversation. Would you like me to host a party on a weekend, or not?