Half the day. Chives are tough. Could probably survive on the windowsill if you have a self-watering pot for them and remember to top it up. Might get a bit brown at the tips in full western sun on a hot day, but will still be edible. They do need to be cut back BEFORE they flower to keep them productive. Even though the flowers are pretty - little pom poms of pale purple. They do need feeding with liquid fertiliser such as charlie carp or seasol or similar for fast growth.