Start with the hours you really have
A two-night stay is not necessarily two full sightseeing days. Before choosing attractions, write down when you expect to reach your accommodation, when you can leave your luggage, and when you must depart for your journey home. Treat travel to and from the city as part of the trip. Avoid assigning a timed admission immediately after an uncertain arrival. The usable time between your commitments is the space your itinerary has to work with.
Choose one priority for each available day. It might be a museum visit, time in a neighborhood, or meeting someone for dinner. Record the date, confirmed start time and any operator instructions for a booked activity. Keep an idea you have not booked visibly separate from a commitment. That distinction makes later changes easier: you can remove a suggestion without accidentally overlooking a reservation.