Q.When is the best time to plant hostas?
do they grow better in direct sunlight?

Most hosta not only prefer part shade, they don't do well in full sun. There are some new cultivars rated for sun but most hosta develop leaf burn in too much sunshine. If your winters are severe, plant in spring to give the hosta all year to prepare sturdy roots for winter. If winters are mild and summers hot, fall planting is also possible, perhaps desirable. All new plants need supplemental water weekly for the first year if rainfall is less than 1 inch. If your soil is sandy or temps are over 90, closer to 2 inches of water may be necessary.