Upvote:4
Should I book with them?
This really depends on your reason for travel and personal priorities.
and How long before the scheduled flight, the airline informs its clients that the flight is cancelled?
Generally it's two weeks. Since it's an EU flight, they would owe you compensation if they cancel less than two weeks in advance so most will cancel only 15 days or so ahead even if they already know they won't fly.
Booking and refunding is still an interest free loan for them and many airlines have currently cash flow problems.