Ideas and suggestions.

so, in OH (Online Hotseat): if both players access the same object, the OH is interrupted – first, Red goes, then Blue, and OH resumes after 3 days;

Blue sees Red's move from the previous day (emulates a real game), and when Blue attacks, Red's turn is rolled back to that day, and OH is interrupted for 3 days.

Red sees Blue's move immediately on the next day.