Hotel de Londres - Bilbao Airport
When you need to go to Bilbao Airport, there is a bus company called Pesa that runs every hour from Monday to Sunday to Bilbao airport, starting at 5AM. It is 1h15 minute drive and tickets cost 17Euros per person.
Tickets can be bought online or at the ticket office at the bus station. The last bus to go to Bilbao airport is at 9 pm.
Hotel de Londres - San Sebastian Airport
When you need to go from the City Center to San Sebastian Airport:
There is a regular bus, number E21 departing from Plaza de Gipuzkoa Square (less than 10 minutes by foot from the Hotel) going to the Airport of San Sebastian. It runs every 45 minutes from Monday to Friday or every hour on the weekends or bank holidays; the ticket costs less than 3Euros per person and you pay directly to the driver (they give you change up to 20 Euros bill) and you would be at the airport in less than 30 minutes, depending on the traffic.