The useful question is not simply how many hours remain before takeoff. It is how much remains after airport travel, airline arrival requirements and luggage collection.
Fix four details first
Write down hotel checkout time, the full flight departure date and time, airport code and terminal. For flights shortly after midnight, check whether departure falls on the next calendar day.
Verify these details against your ticket. Plan separately for airports in the same city: Shanghai Pudong and Hongqiao, for example, need different arrangements.
Make a separate luggage plan
Ask whether the hotel stores bags after checkout, when they can be collected and whether there is a fee. Check airport storage against your bag size, terminal and schedule too.
If bags stay at the hotel, returning for them is part of your day. If they travel with you, confirm capacity for all passengers, bags and child seats together.
Compare costs you will actually add
Day rooms, late checkout and transport serve different purposes. Use a room quote for the period you need; do not simply divide an overnight rate into hours. Confirm room count, occupancy limits and inclusions.
Plan your day compares a private driver with one alternative across costs, time and practical conditions. Do not add transport or supplements twice if already included.
Set a firm airport departure time
Work backwards from the flight using verified time allowances, then use Plan your day to compare arrangements. The remaining window does not guarantee that a particular attraction will fit.
You can rest, eat, walk or head to the airport early. The tool helps organise information; the decision is yours.