I'm easy, any night, even Thursday would be do-able. Return to the Misty Law Mountain Hop possibly or how do we feel about Mugdocks? Or are you thinking further afield?
Tuesday or Wed would suit better and IIRC Tuesday is the longest day. As for destination we'll see whose up for it and take it from there. I did think about Drum but with the weather what it is and for folks to get there after work it could be a stretch.
Google maps says 1hr33m from Erskine to Drumlanrig, so 7.30 should be possible. Fair looking forward to this, haven't been to the Drum at all this year...