Just had to use the lockers a few days ago so I have up to date info:
You can use them for up to 24 hours, so overnight is no problem. They have three locker sizes and you always pay for 24 hrs even if you only need it for a few hours. The cost for 24 hrs are: small lockers 5,50€ (these are big enough for one cabin luggage + carry-on or similar), medium lockers 7,50€ and large lockers 9,50€.
There is a change machine so you won't have to worry about bringing enough coins.
Please note: whatever you want to store inside the locker will have to go through a security scan and some things (e.g. wine bottles) are not allowed!
Hope this helps!