If it is clean, no need to pressure wash it. If it is dirty, being new I would probably a quick scrub with a brush and garden hose. Power washing cedar can do more harm than good. If clean stain it as soon as you can, try and have it be dry and good weather for a couple days of possible.

" Does it need pressure washing prior to staining? " No

" Also is there a certain amount of time to wait before staining? " As long as the cedar timber has been dried, you should stain as soon as possible before any weathering takes place. If you wait too long, you will need to sand or wash it down with a special cleaner before you proceed.

You can test the dryness by placing a small amount of water on the boards - if it beads up, the boards need to dry further and you will need to wait. If the water soaks in, you can stain immediately.