Dinner invitation to Castle Ravenloft

Hello fellow DM’s I’m running a party of 5 thru COS and players are currently at Tser Pool Madame Eva’s tent to get their Tarokka reading. I’m looking ahead and trying to figure out when to invite them to Strahds castle. They are currently level 4 and are escorting Ireena to Vallaki. Ismark stayed in Barovia to govern. They have bonded with Ireena and want to see her safe which I’m delighted they care. They are already thinking Gertruda and Doru have made their way to the castle. They left Doru in undercroft sparing him at request of his father Donavich. However couple nights later he escaped and murdered a local village woman whom I added to story. The party had suspected her making sacrifices to Mother Night in an attempt to save the life of her ill little boy. Any ideas of when might be a good time to drop the invite? Thanks!